[soundnote]

Site isolation is one: Firefox doesn't sandbox websites from each other on non-Windows platforms, and even on Windows its sandboxing solution is just worse than Chromium's. They're doing work on implementing sandboxing more widely, mind, but still have a long road ahead of them to get to parity.

[radlad]

Firefox has had site isolation since 2021: https://blog.mozilla.org/security/2021/05/18/introducing-sit...

[soundnote]

Yes, on desktop. Mobile Firefox still has none, though that should change within this year or the next.