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I really want to use FireFox but it is simply too heavy on resources compared to chrome (running on Linux...Similar experience here.
I run a VM with Linux for development and for viewing videos (e.g. anime). I only use uBlock Origin, NoScript is installed but was quickly disabled because it is too much of a hassle, and I don't care since this is the VM which I use for "pseudo-anonymous" web activities without all my regular logins anyway.
I chose Firefox there just to give it a try. I had to switch back to Chrome. At some point I could no longer watch anime on one site - on Firefox. It still worked fine in Chrome. What happened was that as soon as I started the video the entire browser seemed blocked, comparable to having a way too work-intensive Javascript running. However, Firefox showed me that none of the open tabs incl. the one with the videos had more than 1% of CPU time, plus, it worked in Chrome and that would have been blocked by a runaway JS script just the same. I also don't think the built-in HTML5 video player would be blocked by JS.
I think it was the video that was the source of the block somehow. It took several seconds for any command given to the video to have an effect (play, stop, forward 10s, timeline jump, etc.) The video site used iframes to show the videos from various sources (completely different video domains). Regardless of the source, the behavior was the same.
I gave up, because of the several-second delay of everything debugging was quite impossible anyway. Profiling did not show anything at all. I had to go back to Chrome. This only happened for one (meta) site, it was not a general video issue. I have no idea how I would even debug this, I don't think the regular dev. tools meant for (JS) web dev. were enough here. I made sure I used the exact same extensions in Chrome - only uBlock Origin, with the exact same settings too. So I'm sure the difference was in the browser itself. Similar nr. of open tabs (ca. 10), all but one suspended, on FF using its native built-in tab-suspend (i.e the tab does not load until activated after browser start) so this was not a "huge nr. of tabs" thing.
So unfortunately, at least in my experience, there does not quite seem to be parity between Chrome and Firefox. Also, everything is just a bit snappier now back in Chrome. I sure wish I would not have to depend on a mega monster corporation but I won't go out of my way to achieve that.
Of course, outside this one problem area all worked fine, apart from the bit where Chrome still feels a tiny bit snappier.