Firefox until version 3. Then Opera until around a year after version 11's release; I kept v10.6 due to loathing the GUI rework and disagreeing with Opera's (the company's) principles going forward, but it was becoming increasingly incompatible with websites. Now Firefox again, which I've since found to be highly configurable and nowadays as 'fully featured' as Opera was, so among other things I can maintain a classic Windows 2000 style function-over-form GUI and have multiple instances of the program running. Chrome is a travesty by comparison, or was when I tried it, and I 'distrust' Google, insofar as one has any measure of trust in or respect for a corporation. I don't care about speed or memory footprint.