https://twitter.com/BrendanEich/status/1217512049716035584/p...
https://twitter.com/BrendanEich/status/1217512049716035584/p...
For example just look at the alert popups[0], or the non native contextual menus, or the video pop icon. The UI is full of little quirks like that. The tab bar is by far the ugliest one of all current browsers, at least on macOS.
It also misses important features such as multilingual spell checking. For people writing in multiple languages it's a real PITA. I know this functionality can be added with an extension but it slows down FF too much IMO.
For example, one of the major considerations when doing UI design is creating elements that have a cohesive style (regardless of which aesthetic style that is).
None of that happened on that god forgotten alert. It's probably the first thing that someone came up with in a rush, in a style that no other UI element of FF shares, and it has stayed like this probably because nobody cares.