K-Meleon is an open source browser for Windows that requires less than twice of the resources of Firefox. Also it loads pages as fast as the new Opera 10. So far I find it to be the perfect solution for Windows.
Most of the Firefox extensions can be simply unzipped and added to the K-Meleon plugins folder. A list of useful extensions can be found here.
Ablockplus, syntax highlighting as you type, customizable menus from text files and many others are available.
So far I've seen only a couple of problems in comparison to Firefox. But the required html code adjustments, so that a page is normally viewable under K-Meleon are affordable. Opera and IE are much worse in most cases.
If you are tired from the slow Fox and you are looking for something lighter and user-friendly, simply give this one a try: