They didn't try to, they actually won. Microsoft switching to Blink was had news for Mozilla, and sites that are "optimized for Chrome" started to crop up all over the place. Yes, Firefox is slow on Macs, but you should consider switching to it. We know how it went with IE back then. On Android, the extension support alone makes it so much better than the competition.
When Firefox killed RSS support, they mutilated my bookmarks to remove all of the RSS URLs. Those bookmarks were mine, and Firefox destroyed them without even giving me a chance to opt-out. I can't use Firefox if it's going to do stuff like that. I use qutebrowser, instead.
> without even giving me a chance to opt-out
It didn't flip a pref, the infrastructure behind that feature was removed because it was a maintenance nightmare, and not enough people were using it. You could have opted out (for a while) by switching to the ESR.
I haven't tried qutebrowser, does it have extension or RSS support?