In Firefox, press Ctrl + Shift + A key combination, click the Extensions tab, and then press button.
If you're using Google Chrome, type
chrome://extensions/ in the address bar and then press the icon next to the intended plugin.
In Opera you need to navigate to Tools > Extensions > Manage Extensions and press the Uninstall or Disable option.
Also, you can try to remove them using a plugin uninstaller from the database of Software Informer.