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
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Permite personalizar la apariencia de las páginas y la interfaz de usuario.
The Web Developer extension adds various web developer tools to the browser.
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.
A customizable mouse gestures extension which enables to execute various commands and user scripts with six types of gestures.
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...
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.
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.
Set Default FullZoom Level,
Toolbar buttons for Page zoom and Text zoom.
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 ...
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.