Add-ons I've used and tested and found to be very helpful especially for persons with visual impairments. These focus on a user's interactions with sites and Firefox and not on testing accessibility
19 820 788 gebruikers
Blocks annoying video ads on YouTube, Facebook ads, banners and much more.
Adblock Plus blocks all annoying ads, and supports websites by not blocking unobtrusive ads by default (configurable).
688 756 gebruikers
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.
899 316 gebruikers
Tab Mix Plus enhances Firefox's tab browsing capabilities. It includes such features as duplicating tabs, controlling tab focus, tab clicking options, undo closed tabs and windows, plus much more. It also includes a full-featured session manager.
554 385 gebruikers
The Web Developer extension adds various web developer tools to the browser.
391 700 gebruikers
A customizable mouse gestures extension which enables to execute various commands and user scripts with six types of gestures.
85 984 gebruikers
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.
220 880 gebruikers
The most beautiful yet the simplest add-on that makes a strong colorful appeal. Colors every tab in a different color and makes them easy to distinguish while beautifying the overall appearance of the interface. For Seamonkey & Flock. An essential. F...
314 682 gebruikers
NoSquint allows you to adjust the text-only and full-page (both text and images) zoom levels as well as color settings both globally (for all sites) and per site.
169 074 gebruikers
Adds zoom and rotation functionality for images...
54 675 gebruikers
Set Default FullZoom Level,
Toolbar buttons for Page zoom and Text zoom.
11 061 gebruikers
Wired-Marker(http://www.wired-marker.org/en/) is a permanent (indelible) highlighter that you use on Web pages. The highlighter, which comes in various colors and styles, is a kind of electronic bookmark that serves as a guide when you revisit a Web ...
7 035 gebruikers
Zoom in, zoom out, and reset page zoom with one toolbar button (saves toolbar space). Zoom by clicking on the button, or by rolling the mouse wheel.
6 537 gebruikers
A no-clutter image viewer for Firefox that allows you to zoom, rotate and display images/videos against a custom background. ImageTweak is a must-have addon for any photographer or photography-loving user.