Mobile Safari supports content-blocking now. So, on the iPhone and iPad, that makes it the best browser.
I will stick with Firefox because for me it is one of the best browsers, having used it for many years it looks simple and does what it should with the minimum of fuss.
the code. the code can be forked to to start a new project based on the one it was forked from. icecat and iceweasel are 2 different forks of firefox. basically the code is taken and developed independently from the project it was forked from, so it becomes it's own new project.
As far as I know Mozilla is the best for programming, so for me it means it's one of the best as it has to be really fast for programming. The other one I use form time to time is Chrome.
I used Firefox for a few years but I have noticed stability issues over the last year or two so I've been a very happy Opera user for the last year or two.
I haven't had any issues with firefox, aside from a couple recent crashes ... probably has something to do with the number of tabs I have open. I currently have 75+ tabs open, I had more than that, when it crashed I decided to exit out of some so I'm sure there are times when I have 100 tabs open .. and firefox stays running, sometimes for weeks or months. I'm somewhat surprised that it handles all that so well. TBH though, the real reason I got rid of some of the tabs was because it takes so damn long to scroll through so many of them, leading me to have the same website open in different tabs because I don't realize that it's already open in another tab. Probably not the best for privacy, to have that many tabs open giving me cookies, I have plugins to help with that but then again I use a different browser when I really want to be "private".