I use Firefox mobile pretty much exclusively. I haven't noticed any meaningful performance difference between it & Chrome. It also seems to perform fine on my Fedora laptop.

Mobile is different. I rarely even use mobile. I do however use a lot of tabs on desktop, and Firefox is found very wanting in the performance department.

I don't even think its about number of tabs. Just yesterday and today, Mullvad browser takes minutes to load a set of about 7 pinned tabs (with no other tabs) on startup, whereas Helium (which is based on Chromium) loads in a second or two close to a hundred tabs.

My Firefox currently has 33 tabs open (way more than usual). It opens in seconds on my 9 year old i7-7700k desktop.