Lightweight and basically invisible, when left to its own devices Ghostery will pop up and inform you of just how many trackers/ads/scripts it is blocking, and then retreat quietly back to your toolbar. Customizing your settings is a breeze, and for the occasional time when you want to suspend it, whitelist a site, or whitelist just a particular web plug (on its most severe settings, which I use, it will block Soundcloud embeds, which I wanted to whitelist, for example), a few clicks around in the toolbar menu will have you back whatever you were doing on the internet.

For me it has been a fire-and-forget operation; between Firefox's generally impressive prioritization of security and Ghostery, I have mostly wiped out the internet security concerns that were bothering me. Good stuff.