And now, how about adding browser benchmarks on Linux...? Joking.
Indeed, Firefox is most often used with add-ons: its extension manager makes it easy to download, install and manage these, while Chrome and Opera are best used plain.
@LegendKiller: people say that Firefox is easier to infect because it's now the only major browser without tab isolation and complete process sandboxing (a system that prevents code from running outside the browser's playground, if you will)... Firefox mitigates this by being tightly coded and very reactive against exploits, actually sandboxing the biggest source of exploits (that is, plugins like Flash or Adobe Reader); moreover, tab isolation can be circumvented.
@Nevertell: Tab Mix Plus has been around for a very long time; it was considered for inclusion at one time, but the Mozilla devs refused to make Firefox into a kitchen sink solution: they only provide a platform, users get add-ons for the functionalities they want.
@freggo: your analogy doesn't exactly work, except maybe in the gas VS electric case: VHS was technically inferior to Beta, but was cheaper to implement since Sony asked for large royalties on both recorders and tapes. In the case of NTSC vs PAL, the former predates the latter (BW in 1941, color in 1953) and was made to the best of the knowledge at the time. PAL came later, and tried to solve the problems found in NTSC - please note that you forget SECAM, which had some advantages compared with PAL, and was somewhat compatible with it anyway. In the case of gasoline vs electric, there are 2 problems: the oil lobby is POWERFUL. Moreover, electric still retains a huge problem: power storage.