This is actually unrelated to the CSS lagging on my device, I also write CSS for Firefox’s UI. It’s not meant for 3rd party customization and the ability for customization is behind a configuration flag. With that in mind, Firefox’s CSS just feels very dirty, like its very tricky to figure out how to best change this or that element because of how many moving parts there are between state changes (like :hover) and how variables interoperate. And in some places to make a single change you have to change multiple variables, like if you want to change the height of the URL bar row.
I’ve spent many hours on the CSS, and each time I revisit it, I find that I could’ve wrote this or that better, and I looked for variables that the UI uses, and wonder why I didn’t find them the first time. I’ve been writing CSS on and off for 8 years now, I wonder if I’m just bad it since I’ve never done web dev full time, or it’s actually a lot of work to write good CSS.
I’ve never really worked with CSS but I feel like any skill that you develop, if you look back at your earlier work you’ll find ways to improve it, that’s just kind of how learning a skill goes. That doesn’t necessarily mean you’re bad at it now or you were bad at it then, you’re just human and doing the best you can in the moment.
