If you don't have a GPU...
Most of my browsing is done on an old crappy laptop that sits next to my sofa and only has integrated graphics rather than a GPU.
For years I ran Opera on it until they threw themselves over a cliff by moving to webkit and dropping most of the customisation stuff that I loved. That's when I moved to Firefox as I discovered textensions that allowed me to set it up just the way I wanted.
It seems plenty fast enough for me (especially with Adblock dropping all the crap that really slows most pages down). So no I won't be upgrading this machine any time soon.
I might give it a go on my gaming / work machine, which does have a nice fast GPU. But then again, Firefox already zips along on that machine anyway, so I'm not sure there's a point.