The speed differences are measured in milliseconds.
I'm typing this on FF13, if someone had replaced it overnight back to say FF11 or 12 I wouldnt have noticed
Just use a browser that you like.
I had a shock last night when I discovered that I could not access the AB 'Search Box' at the top of this page and the 'You Tube' box was also inactive. Guess it must have been an AB hiccup because FF13 is now fully operational. However, I have noted that the issue is still with Safari; although Google Chrome and IE are O.K.