We're avid Firefox users here @ TeraScape, and also love the plug-in feature. Here, we try to present some of the more useful addons for your FireFox Browser. But remember, before you use these Firefox Extensions, you'll want to be using Firefox, first.
GreaseMonkey - Lets you customize how sites look & feel, including removing ads, changing the layout of gmail, yahoo mail, google.com & other sites. Learn to build your own GreaseMonkey scripts using Platypus.
Morning Coffee- You have your start pages that open every time you open Firefox. Then you have "Morning Coffee". Maybe on Monday through Friday, you like to read the news, but on Tuesdays & Thursdays, your favorite web comic updates. Click on the Morning Coffee button on your browser, and you'll be taken to all the sites you programmed it to open for that given day.
Anonymouser- You know for a fact that Blogspot is blocked behind the Great Firewall. So are numerous other sites. So why open them in a new tab, when you can simply open them in an anonymoused tab? One simple right-click later, and your Wiki page, Blogspot Blog or other sites are opened up through anonymouse.org.
IE Tab- IE Tab lets you flip back & forth between Firefox & Internet Explorer. IE Tab takes your current installation of IE & simply loads it onto your Firefox browser. Very useful for web designers who need to see what things look like in both search engines.
Customize Google- Customize Google does just that. It customizes Google's various pages, from search to Gmail. With it, you can remove ads, add favicons, and even skip Google's tracking page & go directly to the site.
Access Flickr- Flickr is blocked in regions around the world, including Iran & China. Hamed Sabir of Iran has created this plugin to help people behind these gov't firewalls get access to their flickr accounts & view images from farm1 & farm2.
Adblock Plus, Adblock Filterset G, & Adblock Plus Element Hiding Helper- Yes, you'll want all three to remove ads from web pages. Adblock Plus removes the ad. Filterset.G updates ABP's database on what to search for, and ABP-EHH helps remove even more unwanted elements from webpages.
We have even more on our own computers, but these are the essentials you'll want. Enjoy. For more, head over to Mozilla.org and browse their collection. Happy surfing!