Firefox has a bunch of issues these days, but you cannot overlook Google's use of dominance in search, online docs, mail, and video to push people onto Chrome.

When you're hit with "you should use chrome" on all your most common sites, and the sites you use favor Chrome, it's hard for any browser to compete.

I know people like to bash Mobile Safari, some of which is reasonable, it's really important to realize it's pretty much the only reason sites aren't chrome only at this point.