One thing that was bugging me was how much of the screen some sites were taking up with banners and welcome messages that never change. It means that I have to page down to see whether there's any new content. A great way round this is to use the Firefox extensions Greasemonkey and Platypus.
Platypus gives you a new toolbar from which you can quickly streamline websites & save off the results for future visits. Here's a quick example:
Once you're happy with the changes you've made, hit Save…
Then hit Install. Next time you visit the site, your changes will be re-applied.