Open Firefox
Click on Tools->Options or in Linux Edit->Preferences
Click on the Advanced Tab in the right hand corner
Click on the Update tab in the second row
Below Automatically check for updates to: Uncheck Firefox, Installed Add-ons and Search Engines to disable all automatic updates and check the boxes to enable all of them again. Alternatively you could select what Firefox should do when new updates are found, there are 2 options Ask me what I want to do or Automatically download and install the update
