Firefox Became Irrelevant in the Past Year or Two
And it wasn't unavoidable; Mozilla shot its own foot
Each time a new version of Firefox comes out there are new and unpleasant surprises, i.e. 'features' that exist not to serve the user but to exploit the user for somebody else, even Microsoft.
Mozilla is essentially getting paid to "sell out" Firefox users.
It's hardly surprising that people flock away from Firefox at a rapid pace. Web sites will remain compatible with LibreWolf and other Firefox-like browsers only if Firefox can maintain enough share for webmasters to 'bother' with Gecko/Servo.
At the moment, judging by the screenshot above, Mozilla might not have much time left. Firefox is dying. It's like Netscape two decades ago.
The Web is sadly becoming just a 'transport layer' for one family of browsers or one 'breed' of Web browser. To make matters even worse, many sites no longer deliver any pages; they're just computer programs that render stuff onto a canvas like some virtual machine. Cross-platform stuff is being phased out and standards don't truly exist anymore.
The Web is rapidly becoming what back in the 1990s they excitedly told us the Web would replace. █