I have tried to use FF for year now and I am about to dump it. I want Mozilla to succeed, but there's no way I cold recommend it to friends/family, which is the major thing.

Non-major websites, and even big name ones like Intuit's (quickbooks etc) are constantly having problems. I had to go into settings: just to get into bitbucket in the past week because of some 'referrer' issue

On mobile, it just crashes constantly (e.g. on twitter).