Interface Customizations

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Stylish

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.

Rated 4 out of 5 stars (616)
45,233 weekly downloads

Theme Font & Size Changer No Restart

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.

Rated 5 out of 5 stars (120)
6,350 weekly downloads

Scriptish

The greatest user script engine on the Internet (a fork of Greasemonkey).

Rated 4 out of 5 stars (92)
5,895 weekly downloads

IE Tab + (FF 8+, 7, 6, 5, 4, 3.6, 3.5, SeaMonkey)

IE Tab + is an enhanced version of IE Tab. It supports FF 3.5 or greater, integrates IE Tab with Adblock Plus in the IE Tab engine, and synchronizes cookies between IE and Firefox. You can easily import settings from the original IE Tab into IE Tab +

Rated 3 out of 5 stars (72)
5,391 weekly downloads

YouTube Anywhere Player No Restart

Watch videos anywhere in cinema mode without leaving the website you're on.

Rated 5 out of 5 stars (45)
5,246 weekly downloads

Classic Toolbar Buttons No Restart

'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!

Rated 5 out of 5 stars (100)
3,618 weekly downloads

Forecastfox Weather

Get international weather forecasts from AccuWeather.com and display them in any toolbar or statusbar with this highly customizable and unobtrusive extension.

Rated 4 out of 5 stars (817)
3,312 weekly downloads

F.B. Purity - Cleans Up Facebook No Restart

F.B. Purity hides the ads, app spam and other annoying clutter from your facebook news feed, lets you increase the font size, change colours plus many more features and generally makes Facebook a lot less annoying to use.

Rated 5 out of 5 stars (55)
2,978 weekly downloads

Roomy Bookmarks Toolbar

Make your bookmarks bar better. Roomy Bookmarks Toolbar can: hide bookmarks/folders name, multirow, autohide and many another features(more than 20).
Customize your bookmarks bar using one add-on.

Rated 4 out of 5 stars (169)
2,447 weekly downloads

Restartless Restart No Restart

This 15KB restartless add-on will add a "File" -> "Restart" menu item and a ctrl/cmd + alt + r hotkey to restart Firefox or Seamonkey.

Rated 5 out of 5 stars (136)
2,239 weekly downloads

Customizations for Adblock Plus No Restart

This extension provides various customization options for the Adblock Plus user interface.

Rated 4 out of 5 stars (11)
1,931 weekly downloads

Firesizer

Allows you to resize the window to specific dimensions.

NOTE: Users of Firefox 29 and above must install "The Addon Bar" extension to use this, as Firesizer uses the add-on bar that has been removed in Firefox 29.

Rated 4 out of 5 stars (117)
1,720 weekly downloads

Lightweight Themes Manager No Restart

Manage your installed personas (lightweight themes).

Rated 5 out of 5 stars (3)
1,719 weekly downloads

Nightly Tester Tools

Useful tools for the nightly tester.

Rated 4 out of 5 stars (182)
1,389 weekly downloads

S3.Menu Wizard

Customize menus : Helps removing, moving and renaming menus and menu items
Support: Firefox, Thunderbird and SeaMonkey

Rated 5 out of 5 stars (15)
1,214 weekly downloads

lolifox - Fierr MOD

Replaces the error page with a lolifox appearance with additional features.

A new version 1.0.9.0 (not fully reviewed by Mozilla yet) is available here ( https://addons.mozilla.org/addon/7871/versions )

Rated 5 out of 5 stars (11)
1,003 weekly downloads

Stylish Sync No Restart

Sync engine for Stylish with backup / restore facility.

Rated 5 out of 5 stars (17)
927 weekly downloads

Bookmark Favicon Changer

Right click your bookmark to change favicon.

Rated 4 out of 5 stars (170)
882 weekly downloads

URLFilter No Restart

Block advertisement and access to adult sites

Rated 4 out of 5 stars (9)
868 weekly downloads

FireTray

A system tray extension for linux, allowing to set up custom icon, hiding to tray instead of closing, display the number of unread messages in mailing applications, and other features ...

Rated 4 out of 5 stars (186)
685 weekly downloads