I’ve encountered annoying bugs like Firefox being unable to render elements when SVG filters are applied to them so they just disappear, or smaller things like extreme banding on gradients that no other browser has.

My biggest issue was (maybe still is, I quit using Firefox last year) is that on wide color gamut displays, like every MacBook Pro, it renders colors completely wrong. So it would render literally every website, save black and white website, completely incorrectly.

My main browser these days is Safari (so I’m still enjoying a lot of browser bugs). When I really need something to work or need specific de tools I switch to Chrome. For me Firefox is in a middle ground between those two browsers, resulting in me never actually using it anymore.