I donate to the Mozilla foundation, and I love Firefox a ton. But I can't seem to like the UI by installing a theme, and when I change it to look better the browser slows to a crawl. Does it really matter all that much if I use Chromium?
P.S. To the people from my last post regarding something similar, Firefox was too slow, I'm sorry, but I use Vivaldi instead of Brave because Brendon Eich can suck my dick.
Use Firefox daily at work on three different smartphones over the years and never had any performance issues. In fact, it was usually much faster.
Can't say I know what's going on.