Plugins are extensions on a program making it do more than the current version originally can.
I have a feeling that you are not using google as your search engine. It might look like it, but not actually being it.
Does it say google.com in the URL bar?
If it does: Copy this into the URL bar
chrome://extensions/
And remove what you don't know what is. These are the extensions i was referring to.
---------- Post added at 06:33 PM ---------- Previous post was at 06:31 PM ----------
Ohh i forgot you are not using Chrome.
Do this instead:
1: At the top of the Firefox window, click on the Firefox buttonOn the menu bar, click on the Tools menuAt the top of the Firefox window, click on the Tools menu, and then click Add-ons. ...
2: In the Add-ons Manager tab, select the Extensions or Appearance panel.
3: Select the add-on you wish to remove.
4: Click the Remove button.
(The above is a copy paste from google)