which browser is the fastest?

yes, definitely Opera is the "fastest", but lacks support for addons and stuff like Firefox.

You're right. Opera has more than Firefox "out of the box," but there are more add-ons for Firefox than for any other browser. That having been said, I must confess that I am thoroughly disappointed in Opera 9.5. It has Haute Secure built in, making it theoretically impregnable. But something has apparently gone wrong with the rendering engine or something, as Opera now hangs just like Firefox. Most people are not using Opera or Firefox; they're still using IE. And appropriately so, as IE is (and likely always will be) the most standards-compliant of all browsers. I'm keeping my fingers crossed that Microsoft will not screw it up like Opera and Firefox have been screwed up. Whenever the alternative browsers buckle under the pressure and fail to load a page, IE is the one to rise up to the pressure and get the job done.

Firefox isn't the fastest or the toughest. Opera is the fastest by a landslide, and also the most inherently secure. One nifty Firefox has is NoScript, which can make you pretty tough. But support for ActiveX and other common controls is a vulnerability in itself. Visit the National Vulnerability Database to see for yourself just how much less secure Firefox is than Opera. It's scary!

I'd say Firefox is less stable than IE or Opera. Firefox has a habit of stalling between pageloads, forcing you to refresh two or three times before you can move on. Neither IE nor Opera have this problem, and the latest version of Firefox has yet to address this issue.