Mozilla Firefox is one of the worst web browser I never seen. I used is few days but not now because of many reason. I faces many proble with this browser which are
1) It is more slower than other browser
2)Many times its stop working.
3)Very bad if you open youtube.
4) Its slow down your computer.
Also some more problem I faces for that I avoid to use it. Now I only use Google chrome web browser not any other. Its very fast ant not a single problem with it.