> Firefox deserves to be used more

Totally agree. I even go as far as choosing which website I make purchases on depending if they work on FF, or writing to support occasionally to tell them it's not supported or a feature isn't working properly and this would be appreciated.

I know it pretty much always goes nowhere, but I feel it's what I can do to keep the browser somehow on the radar.

> Firefox deserves to be used more

Part of the problem is, when they stop working on fixing bugs, they start doing Mr Robot things... We just want a web browser. Nobody asked for pocket, or AI...

If they use AI to fix all the bugs, then what else is for them to do, other than maintain syntax compatibility with the various languages they build with? They're just going to go back to making the browser trash again.

Chrome ain't better in any meaningful way for >99% of use cases. Heck, I am a dev and I use FF with ublock origin only, for past... 10 years?

Same with my wife, after I've explained things to her and she understood how different internet experience can be thats the primary browser.

So please don't put the argument like 'here is crappy underdog but please use it because monopoly is bad and google is a bit evil', its first class experience in everything I have ever thrown at it. Tripple that on mobile, by far the best mobile and useful mobile experience, bar none.

Unfortunately we're probably still quite far from that. This is the best case for LLMs still - the quality of their output didn't matter as long as it worked, and there was a near-perfect oracle for checking if their output worked.

That's a really good use case for LLMs. It also applies to things like finding proofs in Lean and creating test stimulus. In both cases you know automatically whether the output is good, and it doesn't really matter if it isn't.

That isn't the case for most bugs, and definitely isn't the case for actually fixing bugs.

Browser haven't needed new features in a very long time. Extensions were supposed to be the solution to that.

Wouldn't that quality and availability just allow Chrome to pull ahead of Firefox that much faster?

If Mozilla created some proprietary LLM or harness that they used internally to outpace Chrome that may be a different story, though I also don't see that happening.

Among other things, Mythos seems better at "let me find, weaponize, and stack vulnerabilities until I get end-to-end from untrusted content to root", rather than just finding one thing in a specific identified area.

Quantifying the abilities of an LLM is a hard research problem, so I'm not sure if I can describe it in any great way, but Mythos did seem to be fairly clever about putting together things from different domains to find problems.

For instance, in one of the included bugs (2022034) it figured out that a floating point value being sent over IPC could be modified by an attacker in such a way that it would be interpreted by the JS engine as an arbitrary pointer, due to the way the JS engine uses a clever representation of values called NaN-boxing. This is not beyond the realm of a human researcher to find, but it did nicely combine different domains of security.

As the person responsible for accidentally introducing that security problem (and then fixing it after the Mythos report), while I am aware of NaN-boxing (despite not being a JS engine expert), I was focused more on the other more complex parts of this IPC deserialization code so I hadn't really thought about the potential problems in this context. It is just a floating point value, what could go wrong?

There doesn't have to be a huge qualitative discontinuity between Opus and Mythos. It's just that Mythos has reached a threshold where it's finally smart enough that putting it in a loop and asking it to find bugs is suddenly really effective. Especially at the beginning, Mozilla wasn't doing anything particularly clever with prompts. Mythos is just smart enough that the hit rate on obvious prompts is high enough to matter. (Maybe you can get similar performance out of Opus 4.6 with really smart prompts, but AFAICT nobody had managed it until Mythos.)

Results similar to mythos have been duplicated by weaker models.

Think it's more a care of mythos raising widespread awareness that tireless LLMs can be weaponized to dig through code and find that one tiny flaw nobody spotted

There is a phase transition where LLMs match or exceed humans' ability to do something, and from that point on, even if the difference between its previous version is small, it will go from something people use rarely, to something that people use all the time.

There was a time when the entire transportation infrastructure in the US was built around horses. Even after cars were invented, the cars weren't obviously better than horses for most people, especially because there wasn't any infrastructure to support them, but the infrastructure and the cars kept improving to the point where it was better for some people at some things, then suddenly it was better at most things, and then people stopped using horses, and we re-organized our entire transportation network around cars.

But there was never a revolutionary technological change. The technology of cars in the 1930s was the same fundamental technology as the cars in the 1890s. Just at some point it became "good enough" and that was it.

I think when people say that AI is a bubble, they are assuming that anything economically useful that LLMs cannot perform today is _qualitatively_ different from what LLMs can do right now, and that LLMs cannot do it even in theory, without some major technological innovation. But I have a suspicion that there are a large number of valuable things, that once LLMs advance just a little bit more, and harnesses and infra around them is improved a little bit more will just be completely taken over by LLMs.

The usual sorts of fuzzing and static analyses, using AddressSanitizer and ThreadSanitizer. Also, with a bug bounty program to try to encourage external researchers to report issues. (I work on Firefox security; also I fixed 2 of the bugs linked in the blog post.)

Coverity (similar to lint) scans various open source software products for vulnerabilities.

see https://www.blackduck.com/static-analysis-tools-sast/coverit...

and for Firefox-related alleged defects, see https://scan.coverity.com/projects/firefox

You have to create an account to view the actual reported defects.

There are just over 5000 reported defects still outstanding. I don't know how many overlap with the reported 271 Mythos-reported defects.

I was a bit confused by your definitions, but here's how Mozilla broke out [1] the 271, um, things:

> As additional context, we apply security severity ratings from critical to low to indicate the urgency of a bug:

> * sec-critical and sec-high are assigned to vulnerabilities that can be triggered with normal user behavior, like browsing to a web page. We make no technical difference between these, but sec-critical bugs are reserved for issues that are publicly disclosed or known to be exploited in the wild.

> * sec-moderate is assigned to vulnerabilities that would otherwise be rated sec-high but require unusual and complex steps from the victim.

> * sec-low is assigned to bugs that are annoying but far from causing user harm (e.g, a safe crash).

> Of the 271 bugs we announced for Firefox 150: 180 were sec-high, 80 were sec-moderate, and 11 were sec-low.

Mozilla uses the term "vulnerability" for even sec-high, even though they say right below that it doesn't mean the same thing as a practical exploit. And on their definitional page, they classify even sec-low as "vulnerabilities" [2].

Words are tools, that get their utility from collective meaning. I'd be interested where you recieved your semantics from and if they match up or disagree with Mozilla.

[1] https://hacks.mozilla.org/2026/05/behind-the-scenes-hardenin...

[2] https://wiki.mozilla.org/Security_Severity_Ratings/Client

Mythos did in fact write PoCs for all bugs that crash with demonstration of memory-unsafe behavior (e.g. use-after-free, out-of-bounds reads/writes, etc).

For us this is substantial enough evidence to consider it a security vulnerability at that point, unless shown otherwise and it has always been this way (also for fuzzing bugs).

> Mythos didn’t write 271 PoC for vulnerabilities

I think the word you're looking for is exploit?

This isn’t true anywhere people have to make decisions about what to work on first.

It may be worth noting that Claude can and will (if it believes you own the code, at least) produce PoC exploits for exploitable bugs that it finds.

My only source for this is personal experience, and no, I can't share any evidence of it.

Both. The skilled will use them to find problems, the unskilled will use them to slopcode insecure software the skilled will have to fix.

That depends on which side has more money.

One of the biggest issues in security historically imo is vendors who think, well nobody will ever find this bug so we can deprioritize fixing it. LLMs will prevent vendors lying to themselves which will lead to more secure software.

In 5 years attackers have an advantage but in the long run I think more secure if developers use LLMs on software to find and fix all of the worse remotely exploitable bugs before release. LLMs are going to force devs to be much more security conscious.

I’m just happy we’re talking about security.

That will make software safer alone.

Kinda like home-improvement stores, power tools, easily available hardware and youtube tutorials led to both incredibly amazing and durable furniture, as well as janky, ugly and even dangerous furniture.

More tools for more people equals more stuff being made on a wider range.

More secure software, but in the same way that the population is net healthier after a plague.

It will probably wipe out a few categories of issues, which is probably a good thing. And those things that still are still insecure can also be translated to some other language.

Translating things to Rust manually was already a thing before LLMs came into the picture. Now with LLMs that's only going to get easier and faster. The long term value is going to come from getting on top of the mountain of technical debt in the form of existing C/C++ code bases that is responsible for the vast majority of memory exploits, buffer overflows, and other issues that despite decades of attention still are being found across major code bases on a regular basis.

Mozilla finding these issues comes on the back of a quarter century of some very competent engineers trying to do the right thing and using all the tools at their disposal to prevent these issues from happening. I have a lot of respect for that team and the contributions it has made over the years to improve tools, testing/verification practices, etc. The issue is not their effort or competence.

The job of taking an existing system that is well covered in test, well documented/specified, etc. and producing a new one that can function as a drop in replacement is now something that can be considered. A few years ago that would have translated into absolutely massive project cost and risk. Now it's something you can kick off on a Friday afternoon. Worst case it doesn't work, best case you end up with a much better implementation.

It's still early days. There are still a lot of quality issues with LLM generated code. But the success/fail rate will probably improve over time.

More secure, at least in the cases where the tools are properly applied.

But it also represents more easily available opportunities for blackhats to abuse against the projects where these tools were not being applied.

Less secure because of all the ways attacks can scale out and hackers can contribute vulnerabilities to active projects.

Mostly I think this just means that having a test case makes it easier to fix and verify. You can't actually take for granted having a test case when fixing a security bug. Sometimes you only have a crash stack or maybe a vague and hypothetical static analysis result.

> eventually land the test case

This is just a reference to the fact that we don't land test cases for security bugs immediately in the public repository, to make it harder for attackers. You are right that the LLM only helps with creating the initial test case. Things like running the test case in automation is part of the standard development process.

The raw number of things found by Claude (Opus or Mythos) was much higher and would be more comparable to a new clang warning. I vaguely remember seeing a number early on in this process that was in the mid-thousands. The 271 is a small, validated subset of that. None of the 271 were deemed false positives iiuc. Most instances of a new clang warning will be false positives. (Same as most of the raw problems reported by the AI.)

It is still unclear and open for speculation as to what percentage of all security bugs in Firefox today are being found by the AIs (as opposed to not being found at all). It might be that AI is very good at certain types of problems, even if we can't put our finger on what those types are, and that after the initial wave of bug reports the AI findings will slow to a trickle even while many many other bugs remain in the codebase. Or it might be that AI really does detect most instances of some class of problems and all those bugs will now be gone forever, never to return as long as Mozilla keeps paying the token monster. This is closely related to the oft-asked question "are we better or worse off after both attackers and defenders have access to this new capability?"

A general limitation of this approach is that it is only as good as your validator, and there's nothing easier to validate than a test case that creates, say, an AddressSanitizer use-after-free. For subtler issues will we have to more specific validators or will the LLM become better at coming up with other dangerous conditions it will verify? We'll see.

It's possible Mythos is a lot better at finding vulnerabilities in C++ code than it is for other languages. After all, these models are also based on pre-existing security analysis.

From what I can tell, a lot of these bugs were hardly C++-specific, they just happened in C++ code. Even the most secure Rust can't magically catch things like TOCTOU issues.

It's because they verified the bugs using AddressSanitizer so by construction it was only ever going to find C++ bugs.

No, it's a new post, see also

https://hacks.mozilla.org/2026/05/behind-the-scenes-hardenin...

The code is open. If you can prove that's the case you'll have a real news story...

More, many more. See the bug reports linked in the post. I checked a few, and all of them had an exploit in them, and there are definitely more than 1 bugs listed.

Well, depending on how you define "exploit"; some might only read arbitrary pointers or just out of bounds. Those would be useful primitives in a chain of vulnerabilities, not exploits themselves. You'll have to read through the first comments yourself, but if you're hoping that this is all nonsense and ignorable hype, you're going to be disappointed.

At the same time other companies like AISLE are matching Mythos on vulnerabilities using older models but their own harnass: https://aisle.com/blog/aisle-matches-anthropic-mythos-on-fre...

So while Mythos certainly is real I think you could do the same with Deepseek pro, GPT 5.5 etc...

> The linked hacks blog

https://hacks.mozilla.org/2026/05/behind-the-scenes-hardenin...

I've been thinking about this. Static analysis tools can also be much faster and most are fully deterministic, so including them in CI can catch bugs or latent bugs before they have a chance to land.

I maintain a static analysis tool using in Firefox's CI. False positives have to be fixed or annotated as non-problems in order for you to land a patch in our tree. That means permitting zero positives (false or true), which is a strict threshold. This is a conscious tradeoff; it requires weakening the analysis and getting some false negatives (missed bugs) in order to keep the signal-to-noise ratio high enough that people don't just ignore it and annotate everything away, or stop running it. Nearly all static analysis tools have to do this balancing act.

AI, as commonly used, is given more leeway. It's kind of fundamental that it must be allowed to hallucinate false positives; that's the source of much of its power. Which means you need layers of verification and validation on top of it. It can be slow, you'll never be able to say "it catches 100% of the errors of this particular form: ...", and yet it catches so much stuff.

Data point: my analysis didn't cover one case that I erroneously thought was unlikely to produce true positives (real bugs), and was more complex to implement than seemed worth the trouble. Opus or Mythos, I'm not sure which, started reporting vulnerabilities stemming from that case, so I scrambled and extended the analysis to cover the gap. It took me long enough to implement that by the time I had a full scan of the source tree, Claude had found every important problem that it reported. The static analysis found several others, and I still honestly don't know whether any of them could ever be triggered in practice.

I still think there's value in the static analysis. Some of those occurrences of the problematic pattern might be reachable now through paths too tricky for the AI to construct. Some of them might turn into real problems when other code changes. It seems worth having fixes for all of them now for both possibilities, and also for the lesser reason of not wanting the AI to waste time trying to exploit them. At the same time, clearly the cost/benefit balance has shifted.

They could also team up: if I relax my standards and allow my analysis to write an additional warnings report of suspected problems, with the clear expectation that they might be false alarms, then I could feed that list to an AI to validate them. Essentially, feed slop to the slop machine and have it nondeterministically filter out the diamonds in the rough.

Food for thought...

LLMs are much better at using tools than replacing tools. The tools are generally a lot faster than trying to achieve the same result with an LLM.

Using LLM coding tools to stay on top of static analysis tool output works very well and adding some guard rails that enforce that there are no issues is probably a good idea. Just like adding CI checks to make sure everything is clean.

As for false positives, it depends on the tool. I tend to avoid tools that generate mostly noise. Most of these tools allow you to disable rules if they produce a lot of noise. Or you can just tell the LLM to fix all the issues. When it's cheaper to fix things than to argue with the rule, just fix it. That used to be really expensive when you had to do that manually. Now it isn't.

I recently did this to an Ansible code base that I needed to refresh after not touching it for a few years. It had hundreds of ansible-lint issues; mostly deprecation warnings and some non fatal other warnings. And 10 minutes later I had zero. Mostly they probably weren't very serious ones but it's a form of technical debt. If you have to fix hundreds of warnings manually, you are probably not going to do it. But if you can wave a magical wand and it all goes a way, why not? I adjusted the guard rails so it now always runs ansible-lint and fixes any issues. Only takes a few seconds extra.

One interesting possibility I've seen discussed[0] is enhancing the static analysis tools to find bug shapes that LLMs originally discover. There's no doubt static analysis tools are faster and cheaper, so they scale better to huge codebases and may allow generalizing the LLM's methods.

[0] https://lwn.net/Articles/1068968/

> What are people's thoughts on how this could affect static analysis tools?

I think these harnesses are _using_ static analysis tools, and probably will continue to do that.

Both are right and it depends on which model you use and who submits those bugs. The capabilities of leading models went from 99% noise to 99% valid bugs in essentially a few months. Some projects are flooded with the former and need to take precautions to avoid essential DoS attacks on the maintainers.

It would be amazing if we didn’t have to have this conversation on every single thread about anything related to Firefox.

Firefox/Mozilla tries literally anything to expand their feature set, customer base, or revenue stream? They need to stop spending money on that and instead spend money on the free product of theirs that I care about, in exactly the way I want.

Google surveilles the entire world, spends huge amounts on lobbying, degrades their own websites on other browsers? Not a peep, usually.

For my part, I pay mozilla for their VPN service, which I’m sure many here would decry as useless spending that should be going to firefox instead.

On both desktop and Android, I've been getting HTTPS errors that require two Refresh clicks before the actual page loads.