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).
Firefox mobile isn't there yet. Passwords will conveniently autofill from your Google account thanks to the Android level implementation of password management, but more importantly it's resource heavy and bad UI design. Ublock support is nice but some websites just don't deal with it well. The nightly builds do fix my main problems with the UI but they crash all the time. So there's hope for the future, but for now it's not great unless you absolutely need proper browser level ad blocking rather than Blokada.