I made a post about Filterset G a few months ago in the Toolbox section, but I will repeat it here, for it is a godly and righteous thing.
Step 1. Install Adblock.
Step 2. Visit
http://www.pierceive.com.nyud.net:8090/filtersetg/ (I always hit the Coral cache instead of the regular page, which I've found isn't always on line).
Step 3. Find the filename with the most recent date (right now it's 2005-09-18a.txt)
Step 4. Right click and "copy link location" or save that file.
Step 5. In Firefox, click Tools, Adblock, preferences
Step 6. In the Adblock window, click Adblock options, Import Filters, paste in the file name or navigate to where you saved it, then click OK, OK or cancel (if you've filtered anything else, choose cancel) then Done.
Advertising is stripped out of almost everything, which makes visiting sites like yahoo.com and download.com a whole different experience.
To take it one step further, you can download the CustomizeGoogle extension, which wipes text ads from google search results as well.