Adblock Plus Get rid of all those ads and banners on the internet that often take longer to download than everything else on the page.
Better Gmail 2 is a compilation of Greasemonkey user scripts that add features to Gmail, improving Gmail's overhauled interface graphically and make it more usable. Each feature can be enabled or disabled.
Download Statusbar Allows you to keep track of ongoing and completed downloads in a hide-away statusbar.
DownloadHelper is for downloading videos and images from many sites with minimum effort. Using DownloadHelper, you can easily save videos from most of the popular video sites. It is also possible to capture all the images from a galery in a single operation. It also gives you access to a big list of video sites where it can be used.
DownThemAll! Lets you download all the links or images contained in a webpage and much more: you can refine your downloads by fully customizable criteria to get only what you really want.
- DragDropUpload lets fill an upload input of a form using the drag and drop service from the system. Just drop the file into the input box and then send it. No more using the Browse button hassle.
FireFTP is an integrated FTP client.
Foxmarks Bookmark Synchronizer Automatically synchronizes your bookmarks between two or more computers running Firefox. It also lets you access your bookmarks from any computer anytime via my.foxmarks.com.
Hyperwords With Hyperwords all the text on the web becomes interactive: Select any word on any page and choose a command.
repagination See more search results etc. on one page, concatenating several pages together. Very useful for forums, where you want to see all posts at once.
ScrapBook [Tips&Tricks about ScrapBook] Helps you to save whole web page trees and manage the collection. You can mark passages of the page, delete content etc. If you used Spiderzilla before, try this one.
- SpamAvert generates temporary e-mail addresses for all those pesky online registration forms.
Tab Mix Plus Enhanced browser tab handling. This is a must-have extension. Tip: Disable Firefox's internal session handling and use the one from this extensions, it's much more powerful.
WebMail Notifier checks multiples of your webmail accounts and notifies the number of unread emails.
This one is much more powerful than Gmail Notifier, because it not only checks GMail accounts, but also Hotmail, Yahoo and several other ones (you can add your own userscripts to support even more).
Note:On Ubuntu you should never install extensions from Synaptic, aptitude or the main menu, because otherwise Firefox's internal extension handler can't update those extensions any longer.