If you're bugged by Web ads, then Adblock Plus is for you. The well-designed Firefox add-on quickly and easily blocks the vast majority of online ads.
The Adblock Plus add-on consists of two parts: a utility to block images, scripts, and Flash; and a subscription component that automatically updates its list of what to block. When you first install the add-on you're prompted to choose a subscription source based on your home country. Choosing a source doesn't require providing any information from you, personal or otherwise; it's there only to pull down a list of online ad sources.
You're prompted to choose a subscription when you first install Adblock Plus, but for most users that will likely be the only choice you have to make. After that, it largely just works.
If Adblock Plus does happen to miss an ad, or if there's a non-advertising image you don't want to see, you can right-click the image display to a new "Adblock Plus: Block image" option to add it to Adblock's list. By default the add-on will block everything coming from the same particular Web location (such as http://images.pcworld.com/images/common/), but you can instead choose to block just that one image or everything from that entire domain.
Since you only get a menu for Flash when you right-click on a Flash object, Adblock Plus will display a small tab on the upper-right of any such item when you move your mouse over it. Clicking the tab offers the same block options as right-clicking an image.
A red stop-sign icon icon on the right side of the Firefox navigation toolbar offers a route to other nice options. A left-click displays a list of all the blockable items on your current page, with blocked items listed in red. Right-clicking the stop sign allows for turning off Adblock Plus for the currently viewed site or page, or disabling it entirely.
Adblock Plus does its job very well. It works smoothly right away with no work required, and also offers advanced customization options for those who want to dig in. If you want to stop seeing ads in Firefox, this is all you need.