Is there a good reason for this? I would think that a security issue should be addressed and patched into user's computers as soon as possible, especially something like RCE.

Security fixes carry the usual risk of regressions (even more than the average bug, when the fix limits something that used to "work"). Therefore they need just as much bake time as other kinds of changes.

Also, shipping security fixes in stand-alone updates makes it much easier for attackers to identify security-critical changes (especially if they have access to source code, which they do for Firefox) and reverse-engineer the flaw. Firefox developers often land critical fixes with somewhat obscured commit messages to increase the work required by attackers to identify the critical security fixes in the torrent of commits that go into each regular release.

Obviously this only makes sense while the bug is believed to be unknown to attackers. If Mozilla believes the bug is being exploited, they can and do issue an emergency update.

> Firefox developers often land critical fixes with somewhat obscured commit messages to increase the work required by attackers to identify the critical security fixes in the torrent of commits that go into each regular release.

Wow, that's fascinating. Do you have any interesting reads to point to in this regard?

Do you know why? Isn’t a security fix a bug fix?

Nope. Security vulns are not regressions!

And how do you qualify "Meltdown" and it's notorious bad fix "Total Meltdown" in that case ?

To me, the bug fix introduced a clear regression, allowing an even more powerful vuln in the process.

I’m confused what do you mean? Fixing security vulns can often times lead to regressions since overtime users become dependent on a behavior that relies on a insecure behavior.

Secure behaviors should generally trump API guarantees.

Your parent comment didn't say security fixes couldn't lead to regressions, they said security vulns themselves aren't regressions.