As long as we agree that IE is not usable, there is nothing egregious about using Firefox. For instance, my fiance can't use chrome and absolutely hates it, and is currently surfing the web on firefox right next to me - no matter how many times I have tried to convert her. She isn't a technophobe either.
As an aside, for the first few months using chrome, I kept bookmarking things in firefox, and was using it solely as a bookmarking tool because Chrome's bookmarking system is retarded. I have stopped doing that because it is a pain in the ass, and have just organized by bookmarks better. Still sucks.