I made a conscious attempt to try to switch to Zen (built on Gecko/Firefox), but ended up switching back to Chromium-based browsers because pages just feel like they load faster with Chromium. :(
Zen is my favorite browser experience by far, and I've been using the web since Netscape in 1994. But the slowdowns do put a damper on things. Also some of the streaming platforms don't seem to play nice with it.