I switched to Basilisk when Firefox 51 wasn't usable anymore, then few years later to Pale Moon. There's been few hurdles along the way, mostly related to JavaScript monstrosities dominating post-Chromeopalyptic web. Need backup for few specific sites, mostly work related.
But otherwise, my web life is still like as if Firefox never dropped its extensions, NPAPI (Flash Player, ability to use professional application for PDF viewing inside browser tab...), no tricks needed for tabs below address bar, have working ColorfulTabs extension, GlassMyFox (Aero Glass is dead on Firefox, on Pale Moon, it still lives, even on Win10+ with DWMBlurGlass), no need to deal with CSS for UI customizations that breaks all the time on Firefox (or userchrome scripts), navigational sounds just like in Windows Explorer or Internet Explorer (Navigational Sounds extension), font rendering that still obliges Windows ClearType settings and probably some other things I forgot.
Still daily driving 16,5 years old AMD based PC, I notice other browsers, despite being snappier at first glance, put notable stress on the machine. Firefox does take a good long while before it's ready after the window opens, Edge seems to cause occasional audio dropouts. TBH, I haven't messed with other Chromium browsers in a while, Edge is the only Chromium browser with tweaks to font rendering to consider ClearType settings and Firefox is usually good enough as a backup, haven't come across anything that would only work in Chromium. Plus Edge is from Microsoft and we don't want to deal with Microsoft more than we have to, right. 😜 Though Chromium is still interesting to play with when it comes to specific demanding applications.
It'd be nice if we could cover certain aspects with extensions in Pale Moon, but the wizards who can program them are few and far in between. There's a notable gap with things that are still doable in web extensions.