I had a similar problem with Owl, it's because they typically use CSS filters to achieve dark mode. It's frustrating because it's a very bad solution but it's easy to not realize that the extension is causing the problem (especially because browsers work hard to hide it)
That does show up one area that Chrome still eclipses Firefox - the Shift Esc task manager that will usually reveal which tab or extension is cratering things. Firefox is much more opaque about memory and especially CPU use, making it far harder to pin down.
I have a hope of remembering about:performance. I can bookmark it, and it's there in autocomplete. You can make a link to it in your webpage or in a nice plugin (which, once it gets a couple thousand users, you can sell to an honest businessman for tens of thousands).
Shift-Escape? what? I'm supposed to just randomly press every key combination till something happens?
I reset Firefox recently on an ancient Linux laptop and before I got uBlock origin set back up the browser was nearly unusable. I had taken for granted how much it was doing. If I ever get out of this deep financial hole I am sending gorhill a large donation (if he accepts, I recall in the past he wasn't taking any). One of the most, if not THE most useful QOL add-ons in my view.
Dark Reader which is one of my must-haves has a known Firefox performance issue on a LOT of sites that makes Firefox almost unusable for me, so I recently begrudgingly switched back to Chrome.
>Unfortunately Firefox is terribly slow in unpredictable places. I periodically try to find out what exactly makes it work slow in Firefox. For example this change improved twitter.com loading from ~30s to ~1s.
His change[0] was changing array population from repeated concat to push. This is not an unpredictable hot spot but a developer not knowing his tools. Common sense is not premature optimization.
There's a fair few others that can upset Firefox but never seem to be the same extent of annoyance for Chrome.