Accessibility Help Page
Here is where you can get help and the proper tools for your browser to enable accessibilty features if you do not already have them.
First what you need to do is go to this site and check to see what extensions and plugins need updating in FireFox.
Firefox plugin check and update page.
https://www.mozilla.org/en-US/plugincheck/
After that goto this link to get and install any missing accessibilty plugins and extension you may require.
Firfox accessibility extensions page
http://www.accessfirefox.org/Firefox_Accessibility_Extensions.php
Here are the direct links for both the Zoom Buttons and Screen Reader for Firefox.
Firefox accessibility extensions links.
Page zoom buttons for Firefox.
http://www.accessfirefox.org/Page_Zoom_Buttons.php
Reader for Firefox
http://www.accessfirefox.org/Reader.php
This page for Firefox gives you accessibility feature guides and tutorials for Firefox.
http://support.mozilla.org/en-US/kb/Accessibility
Google Chrome accessibility features.
Got to this page if you are using Chrome and need added features.
https://sites.google.com/a/chromium.org/dev/user-experience/low-vision-support
This page will give you the required screen readers for many of the available browsers.
https://sites.google.com/a/chromium.org/dev/user-experience/screen-reader-support
Opera Browser.
This page gives you tutorials and guides on how to adjust the available features in Opera.
http://www.opera.com/support/kb/view/164/
Finally the well renowned Internet Explorer from Microsoft.
This page has about the only extra add-on available for IE its called the Web Accessibility toolbar for IE 2011.