Nuke internet ads using Firefox add-ons
Next, install the Adblock Plus add-on for Firefox (but DON'T install the Adblock Filterset.G Updater). Adblock Plus automatically removes most ad content from web pages you view, either leaving white space or collapsing the content down to cover the white space (depends how the page is designed). It updates its ad filters through subscriptions; by default, it's subscribed to only one ad filter, but you can add more (but be careful, as each filter slows down your browser a little more). If you see an ad that Adblock Plus doesn't catch, you can also right-click the ad and choose "Adblock image". You can also modify the options for Adblock Plus, allowing you to add URLs with wildcards (*) to remove ads that the ad filter missed. Voila!
Next, install the CustomizeGoogle add-on for Firefox. This one removes all Google ads from the side of Google search results, Gmail, and many other places. You'll want to modify its options through Tools...Add-ons...Options or through Tools...CustomizeGoogle Options, to make sure it's removing the ads from all the pages you want it to. The default is to leave some ads visible, so you'll need to select the right check boxes.
There are lots of other cool add-ons for Firefox... check them out. Some other good ones are McAfee SiteAdvisor and Tab Mix Plus (including the options for restoring your previous session).
Good luck!