Certainly, there are various Google+ extensions for Google Chrome browser unlike Firefox. I just came to know about a Firefox add-on which is actually not related with Google+ but just lets you easily +1 any site or webpage directly from address bar in Firefox. The +1 button is a shorthand for “this is pretty cool” or “you should check this out.”
Plus One Button extension for Firefox lets you recommend any favourite site or interesting stuff by clicking the +1 button from address bar. You can +1 any webpage using this add-on without waiting for the webmaster of the site to add +1 button first. The +1’s made using this extension appears in the +1’s tab on your Google+ profile. You can do +1 and Undo +1 using this button (shows +1 counts too). Your +1’s can help friends, contacts, and others on the web find the best stuff when they search Google.
Link: Plus One Button Firefox Add-on