So maybe my experience is unique but websites don't always test with Firefox now and some simply don't work with it. I use it anyway out of principle but occasionally I need to open Chrome.
On mobile it's even worse. Firefox is stuttery on my Pixel 8 Pro and doesn't handle more than ~20 open tabs well. The nightly version fixes the stutter but crashes all the time (it's a nightly build after all so this is expected).