After upgrading to Ubuntu 16.04 I noticed my usual middle-click behaviour on Firefox had changed - instead of enabling auto-scroll it was attempting to navigate to strange urls.

Normally Ubuntu will try to paste the contents of the clipboard when you click your middle mouse button. If you’re currently in Firefox and you do this it will try to open what you pasted as a URL.

To revert to middle-click scrolling:

  1. Go the the advanced preferences page. To get there, type about:config in the Address Bar and hit enter.

  2. In the preferences search bar type middlemouse
    1. Change middlemouse.contentLoadURL to false.
    2. Change middlemouse.paste to false.
  3. Type autoScroll into the preferences search bar.
    1. Change general.autoScroll to true.
  4. Close the browser and restart.

Middle-click scrolling will now be enabled again.