This actually only happens when you update Firefox through your distro's package manager when its running (or your distro updates automatically in the background).
That makes more sense because I've never encoutered this bug but my distro doesn't have a Firefox package, I use the "Windows" distro from Microsoft. Very stable and highly compatible anymore.
Unfortunately your distro decides when software updates and leaves very little in your control. Not very stable if it is updating things without your permission.