Which browser?

Firefox is too slow and bloated. I use Chrome - it does everything I liked firefox for, but leaves off all the crap. It is also much much faster - particularly on javascript-intensive things.

Except it doesn't have extensions.

And I am far too accustomed to not seeing adverts on the internet.

And I'm not sure I can do Gmail without the Better Gmail 2 extension that gives me Folders4Gmail, favicon updates, etc.

And that's before the userscripts.org customisations.

Oh... and if you're bleeding edge, the latest version of Firefox compiles the JavaScript too, so speed is relatively similar.