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.