addons i've found while looking for something else, but found to be worth looking into,,,, later when i'm Not looking for something specific to accomplish whatever it is i'm trying to do
Restyle the web with Stylish, a user styles manager. Stylish lets you easily install themes and skins for Google, Facebook, YouTube, Orkut, and many, many other sites. You can even customize Firefox and other programs themselves.
Squared tabs, appmenu, add-on bar, small button view and many more 'old' features for Firefox 29+ (Windows / MacOSX / Linux).
All builds & changelogs on versions page!
Lightbeam is a Firefox add-on that enables you to see the first and third party sites you interact with on the Web. Using interactive visualizations, Lightbeam shows you the relationships between these third parties and the sites you visit.
AiOS lets you open various windows as sidebar panels, and quickly switch between them. So it put an end to the window chaos! In addition to bookmarks and history it opens dialogues such as downloads, add-ons and more in the sidebar.
Debug Flash/SWF files on the web. Edit properties and inspect elements on the fly. View log output inside the extension. Run AS3 code against the active SWF. Access assets with the Explorer. View AMF calls and Shared Objects and much much more...
Displays tabs in tiled layouts in Firefox. Arrange tiles horizontally, vertically or in a grid. Resize tiles by dragging splitter bars. Tabs and links can be dragged to open in other tiles. Supports multiple tiled layouts. Works with tab groups.
Integrates location bar and search bar into one. Shows search and url suggestions. Quickly switch search engine using search keywords. Provides different auto-complete popup styles for compact displays.
Adds toolbar buttons to the customize toolbar window in several programs including Firefox, Thunderbird and SeaMonkey. Some of the buttons make commonly preformed actions quicker, others add new functionality.
'Classic Toolbar Buttons' add-on restores old toolbar button ui (known from Fx 4-7s small view, Fx 4-12s large view & Tb 5-14) for current Firefox, Thunderbird and Seamonkey versions on Windows.
Beta builds on versions page!
Plugin for downloading video from VKontakte.ru / vk.com social network.