Theme Font & Size Changer lets you change the global font size and font family used for the user interface in Firefox. Design your browser with your favorite font.
Makes every page to have light text on dark background (exact colors are customizable)
Firefox version is here: https://addons.mozilla.org/firefox/addon/dark-background-light-text/
Flexible Sidebar allows to change sidebar width by dragging the handles.
SeaMonkey Vertical Tab Bar Requires Restart
Tab bar on the side of the window for SeaMonkey.
A full featured color selector tool, to work with colors, and easily find the colors you want.
YouTube Video Player Pop Out lets you pop out YouTube videos so that you can watch YouTube videos while you surf.
jsbtn Requires Restart
JS on/off status bar button
Tategaki Requires Restart
Tategaki allows vertical writing-mode on mail compose window.
This extension makes browsing for extensions easier at addons.mozilla.org. It fixes incorrect information about some extensions being not available for SeaMonkey and adds links to the Add-on Converter where needed.
Restart Application Button lets you restart your Firefox and SeaMonkey application by a quick toolbar button click.
Add-on for Thunderbird that replaces the built-in notifications with OS native ones. It supports most Linux Desktop Environments as well as Windows 8.1/10.
GNOMErunner Options Requires Restart
Allows to customize GNOMErunner theme
Stylish-Custom Requires Restart
custom additions to Stylish extension
Speed Dial & Start Page with flexible layout for fast access to sites via visual bookmarks
A button to be able to open the profile folder, along with two buttons to create profiles, and also switch the current profile.
Restores version numbers for all installed add-ons inside Add-on Manager on Firefox, Thunderbird and Seamonkey.
Show all the menus in a single menu button that can be placed anywhere. Also contains replacement buttons for the default menus.
Adds buttons to toggle the using the default page colors and fonts, and the page defined colors and fonts.
Adds a few buttons to help with page navigation, including Page Top, Page Bottom, Page Down and Page Up.
Keeps track of your browser tab number.