I tried it on a Galaxy Tab s5e and an LG v35, which have last year's mid-range Qualcomm chip and 2018's high-end chip respectively. On the v35 loading was slow, and sometimes it would crash or make all my tabs blank until restarted. On the tablet it couldn't even scroll down a page without lagging. I haven't run into any other apps that do this on either device. Zooming was always laggy and a bit off--bad acceleration curves or something--enough that they've redone it from scratch for other platforms instead of trying to fix the code.
There's a reason Mozilla is rewriting the whole thing.
That's crazy =(
That LG v35 outspecs my BlackBerry KEYone by a good margin, and Firefox is just as fast as Chrome for me. Which is to say, snappy.
I read more details about your performance problems in another comment, and it sounds horrible; I can't imagine anyone using that. Sounds like a nasty bug, I guess..?
(I don't use uBlock on mobile, but I might go look into it...)
My only complaint is that it doesn't integrate quite as well as Chrome, but I don't think that's Mozilla's fault.