This is on the nightly version:
Wiki page - it’s basically process isolation, which is AFAIK the main blocker for why their mobile browser isn’t recommended by PG yet so it’s good that it’s finally almost here.
Where are you seeing this page?
Fission is not enabled for me yet.
You have to press the Firefox nightly logo multiple times and then you can see this in Nimbus experiments.
Probably same as Ironfox (Firefox on Android) now has enabled early-stage Fission (per-site isolation)! - #3 by sha123 though, but it’s a good sign
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Yeah, they still have some performance improvements to do, that’s why they aren’t rolling out more widely, see the blocking issue on 1610822 - (gv-fission) [Meta] Make GeckoView Fission Compatible
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@Alvah.Lind64 check process structure and Selinux context for Firefox processes via ADB. I doubt that anything significant changed.
isolatedProcess issue tracker: 1565196 - [meta] Enable android:isolatedProcess on GeckoView
There is so much more wrong with Firefox on Android.
Where exactly?
Please share the reason when you defend something.
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No JIT sandbox, no content sandbox, no site isolation, no security-focused memory allocator, no BTI, no PAC, no type-based CFI, and so on…
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Project Fission is site isolation..
Assuming this mean Branch Target Identification, Chromium Indeed has support for it while I see no mention of Firefox having it
I think that you could file issues/feature request for PAC and BTI. They are slow but they do care about improving security IMO.
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FF on Android does not have site isolation as of now, no matter what it is called.
Feel free to do this yourself. I would be surprised, if they didn’t follow new ARM feature announcements or didn’t have a look into what Chromium is doing.
They care so much, that they are many years behind and still keep falling behind more.
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Well that’s what this post is about right? That site isolation is coming soon.. A step in the right direction. Try being positive, makes life more fun probably 
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PAC: 1671152 - Investigate enabling pointer authentication on ARMv8.3
BTI: https://bugzilla.mozilla.org/show_bug.cgi?id=1626955 (BTI is extremely similar to IBT)
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There is no evidence for that. You either do not understand it or you did not check their issue tracker.
This is a technical problem and not a matter of attitude.
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Sorry to barge in, but no evidence that they’re rolling it out? Or that Fission is site isolation?
Either way, you’re incorrect, because at the very least there is a rollout to Nightly users, as evidenced by OP, and also the Mozilla Wiki page I referenced directly calls it site isolation.
Firefox is, in fact, missing security features, some of which you mentioned, but isn’t this a step in the right direction?
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Don’t twist my words. I said that there is no evidence of site isolation coming soon. Their issue tracker still has important blockers which won’t go away soon and their current state of Fission on Android does not provide site isolation, because they are not sandboxed. Ironfox already has Fission activated, but there is no site isolation.
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Apologies if it seemes like I twisted your words, I was just asking for clarification to understand which point you were trying to make. No malice intended 
After inspecting the currently open blockers for Fission, it seems like none are directly related to the actual sandbox. Maybe you meant that they don’t implement isolatedProcess? If so, that is unrelated to site isolation.
Per the Android documentation:
If set to
"true", this service runs under a special process that is isolated from the rest of the system and has no permissions of its own. The only communication with it is through the Service API, with binding and starting.
If so, it seems like they are actually just missing performance work and Fission/site isolation should be fully implemented in GeckoView, with nice-to-haves and additional features implemented later.
What exactly is missing? Is there any specific bug you meant?
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This one seems to be for desktop as Intel has no smartphone chips.
Are you saying fission≠site isolation, in which cases how would you define Fission?
The only technical issues to rolling Fission to GeckoView is performance issues.
Matching a giant corporation like Google isn’t easy. But they do care about privacy, as outlined by for example : not allowing unsigned extension in standard Firefox, not even in developer settings, using their own certificates instead of the system, a lot of DNS options including forcing the system to use them, etc.
That’s not to say that Firefox is more secure than Brave, it’s not. But saying they don’t care just doesn’t reflect reality.
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ARM’s implementation of forward edge integrity (BTI) is extremely similar to Intel’s setup (IBT). They’re even used exchangeablely in the issue
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Matching a giant corporation like Google isn’t easy.
Not like they have multiple hundred millions of dollars or anything… From a small indie startup like Mozilla we should have realistic expectations.
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You simply assume that a very early test version does in any way provide meaningful site isolation. They might just test small parts of it, without providing any meaningful security improvement yet. Just because they have a toggle written Fission on it does not mean that it is providing any meaningful site isolation in its current state on Android.
They are not close to providing site isolation Android, which is what matters. They didn’t even sort out how to properly sandbox their browser.
@sha123
What browser do you recommend for both strong security and effective ad blocking?
Brave has strong ad blocking, but it lacks the CFI and MTE features of Vanadium for example.
Unrelated, why doesn’t Brave provide a Tor mode on Android like they do on desktop??
I wish we didn’t have to use the insecure Tor Browser for Android.
I tested site isolation on IronFox, Fennec and Mull following the method outlined by a member of the Chromium surveillance team.
Basically, and as expected IronFox (and Fennec) have a process for each sub-frame, while doesn’t as it was last updated in 2024 and therefore doesn’t contain the Fission changes.
Feel free to explain why Fission as described here isn’t site isolation.
See screenshots:
Ironfox
Fennec
Mull
Edit: I messed up the second collage (website screenshot is actually from IronFox), but most important is just noticing they are subframe
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