Here's a list of firefox add ons that give alot of control back to the user.

User Agent Switcher

https://addons.mozilla.org/en-US/firefox/addon/59

Yout browser identifies itself to a webserver with each page that it fetches. Sometimes a web server may deny or grant your request based on this useragent string. A site may choose not to "support" a certain browser or it may let googlebot see its pages without logging in. This plugin lets you change the useragent so you can masquerade as another browser.

RefControl

https://addons.mozilla.org/en-US/firefox/addon/953

In addition to the useragent string, the browser tells the webserver referrer, which is the url of the page it followed the link from. Once again the webserver may deny or allow your request based on this string. I have seen some braindead authentication schemes that just rely on the referrer. With refcontrol you can control what referrer gets sent on a per site basis.

NoScript

https://addons.mozilla.org/en-US/firefox/addon/722

No script lets you whitelist or blacklist sites that should be allowed to run javascript and other embedded stuff. Just by enabling noscript you will remove most of the advertisements from sites that you visit. No script can also break functionality so if a site doesn't seem to be working correctly, add it to the whitelist.

BeeFree

https://addons.mozilla.org/en-US/firefox/addon/57131

Most search engines track what links you click on in order to measure their popularity. If you do not want to add your browsing proclivities to the vast amount of data that google already has on you, enable this plugin. BeeFree will break the javascript link click trackers on popular search engines and will remove the referrer on requests that you follow from the search engine so third party webservers won'
t know the search terms you used.

Javascript Bookmarklets

https://www.squarefree.com/bookmarklets/

This is not really a plugin, but it can make your life easier and fight evil. These are little snippets of javascript code that you add to firefox just like a bookmark. These bookmarklets do things like open all the links in a page, or make tables sortable. You really have to play around with these to see what is possible.