I left firefox after 4.0 debuncle. Yes it was the first release to really support HTML 5 but it was freaking HORRIBLE. Bad UI, sloooow, and on older hardware it was unusable. IE 9 won rewards on tomshardware.com which was released march 2011. I held my nose and gave it a try. It supported hardware acceleration, html5 (I admit it was more limited at the time), and was great on my 6 core system as it has per process tab. Since 2001 it ran circles on gecko web engines??!
Many slashdotters said ewww no thanks based on IE 6 memories.
I then played with Chrome. Yes it is spyware somewhat but it too has important features and has less hardware acceleration but it is more secure and frankly a much better browser than Firefox.
My father got hacked with Firefox. It is a shitty browser with no lowrights mode. It is frome the XP era and has no concept of %appdate and uses the filesystem and has access rights to some processes and threads. Bad security wise but that is what XP era software did.
Chrome and IE 9+ have separate code bases for this with XP vs Windows 7 and greater with sandbox support. Many here use Comodo Dragon which is based off of Chrome but has no privacy issues. However, be warned it based off the previous version of Chromium with some security holes.
Switch my friend!
Until Firefox goes to a processing model and supports lowrights mode I will not go back. This may change hopefully as Firefox is improving with performance and ram requirements since 2011 but on a 6 core system it is stupid not to multitask!