Below is some best firefox add ons free you must have.
StumbleUpon. This add on gives you only the best internet has to offer.
Colorlicious. This add on allows you to change the color and appearance of Firefox.
TinyURL Generator. This add on allows you to quickly generate a small URL for any page.
Best firefox add ons free you must have for security
WOT. This add on displays a warning screen of a web page if it’s insecure.
Omnibar. This add on runs URL bar into a Google search as well as the address bar.
AutoCopy. With just highligting the text will immediately copy the text, without having to right-click and select copy.
Adblock Plus. This add on can remove any ads that can bother you browsing.
DownThemAll. This add on can manage downloads and increase download speeds.
TimeTracker. This add on allows you to keep track of how much time you are spending in Firefox.