Top
Best
New

Posted by HieronymusBosch 1 day ago

Hardening Firefox with Claude Mythos Preview(hacks.mozilla.org)
https://arstechnica.com/information-technology/2026/05/mozil...
356 points | 159 commentspage 3
kittikitti 1 day ago|
This is great, and it reflects some of the changes I've seen in the changelogs of Firefox and many others that have utilize Mythos. I'm closely watching a supposed data wall for AI models and this is a clear indicator that AI capabilities can still become much more advanced even at this point in time. It makes me enthusiastic about future releases and optimizations. Thanks for sharing.
mmooss 1 day ago||
> “That’s the key thing that has unlocked our ability to operate at the scale we’ve been operating at now,” he said. “It gives the engineer a crank they can pull that says: ‘Yep, this has the problem,’ and then you can iterate on the code and know clearly when you’ve fixed it and eventually land the test case in the tree such that you don’t regress it.”

I don't understand much of this paragraph:

* "a crank they can pull that says: ‘Yep, this has the problem,’": as in, ring an alarm? Does the LLM ring th alarm?

* "you can iterate on the code and know clearly when you’ve fixed it": Isn't that true of most bugs, assuming you do the normal thing and generate a test case? And I thought the LLM output test cases itself: "It will craft test cases. We have our existing fuzzing systems and tools to be able to run those tests" And are they claiming the LLM facilitates iterating?

* "and eventually land the test case in the tree": Don't you create the test case before the fix? And just a few words earlier they seemed to be working on the fix, not the test case. And see the prior point about test cases.

* "such that you don’t regress it.”: How is the LLM helping here?

Maybe I'm missing some fundamental unwritten assumption?

mccr8 1 day ago|
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.

mmooss 1 day ago||
Thank you; that makes sense.
ChrisArchitect 1 day ago||
Related:

The zero-days are numbered

https://news.ycombinator.com/item?id=47853277

rem1099 1 day ago||
I don't find that number very high. In a project of the size of Firefox, a new version of a compiler with stricter warnings or a draconian interpretation of the C standard can easily find 200 new bugs.

New tools find new bugs, but the oligarchy newspapers report on Mythos and not on clang-22.0.

sfink 1 day ago|
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?"

legacynl 1 day ago||
Mozilla is always looking for new revenue, how likely is it that Anthropic payed for this article?
Worf 1 day ago|
Maybe if Mozilla focused less on new useless features and redesigns, they would be able to focus more on writing secure and bug-free code.

I'm not only talking about big things like

* Pocket,

* several major UI redesigns and

* the offline translations,

but even tiny useless things like

* browser.urlbar.trimURLs,

* putting the search query in the URL bar instead of the URL after searching from the URL bar,

* messing with the Edit and Resend feature for no reason (the good one that updates the content length is still available at devtools.netmonitor.features.newEditAndResend) and

* probably thousands of little shit like this that took a bunch of developer hours to implement.

All of the above should've been add-ons.

And of course, we know Mozilla spends a lot of money on things unrelated to Firefox at all. It's amazing Firefox is somewhat secure and stable compared to Chrome, which is backed by Google with their infinitely deep pockets.

This is a web browser, after all. Something most people use all the time. Something that accepts untrusted input from thousands of sources every day. People use it pretty much every aspect of their lives - banking, personal communication, porn, expressing political opinions. It's used for viewing PDFs, playing media files, for interacting with a whole bunch of APIs (that IMO shouldn't be part of the web, but they are). Security should be top priority.

mplanchard 1 day ago|
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.

Worf 1 day ago||
> It would be amazing if we didn’t have to have this conversation on every single thread about anything related to Firefox.

If Firefox starts acting maturely, we can stop having these conversations. Until then we see useless crap in every update while most bugs don't get any meaningful attention. Some changes even made things worse than they were before, for example the new Edit and Resend (not so "new" anymore). If Mozilla starts acting the best interest of the user, stops with the ad BS and doesn't try to be everything all at once and actually focuses on Firefox, I would donate. And so would others. If I donate now, I doubt even 1% of my money would go to anything meaningful, like bug fixing.

> Not a peep, usually.

No, fuck Google and Chrome and even anything Chromium-based. Here's the peep from me.

> 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.

Does the profit from the VPN service go to Firefox? If not, what's the point of having a VPN service.