> Firefox in Firefox OS was slow and it gave me a feeling that firefox was not for mobile (but I guess it's not true anymore)
I genuinely don't understand how Firefox on mobile is slow. I hear this complaint often (along with the complaint of Firefox on desktop not being able to run certain websites, which also never occurs to me), but for how much I try, I never managed to make Firefox on mobile (android) slow. There were a couple of days not long ago (we are talking weeks) were after an update the browser did get indeed a little slow, but it was still usable, and it got fixed very quickly.
I use the hell out of my Firefox, both on desktop and mobile. I abuse it in all sorts of ways, and I am extremely demanding of it, yet it never breaks a sweat. Right now I have more than 100 tabs open in my Firefox on android - can't tell the exact number because when the 100th tab is opened, the number just becomes an infinity symbol - which is nothing more than average for me, I can easily get to 350, and it still opens and loads up instantly (at the time of the performance problem mentioned above I had ~260 tabs open).
Am I just lucky? Do the performances/usability change so vastly from phone to phone and person to person?