But good point, there would need to be a "security" switch or else, that you select and that actually hardens the browser.
Vanilla should always work, and I agree I sometimes need a vanilla profile.
Firefox profiles are also horribly integrated into firefox. Like there is no GUI way to switch them, without entering "about config". People think Firefox has no profiles and think thats a Chrome thing, which is fucked up as Chrome copied that
There is a profile GUI but it's true that it isn't integrated into Firefox. You have to start it with firefox -ProfileManager. On Windows I recall it used to add a start menu entry for it but not on Linux.
Firefox Flatpak, RPM, and Windows have this entry. firefox -p is enough and works cross platform.
But it is no button so people dont think it exists. I heard tech people say "Chromes profiles are better than Firefox containers" as they literally didnt know this core feature.
Thunderbird has profiles too, Element web also. Both have no GUI at all.