Revert Site by steeev+

Revert Site makes Facebook think you are using an old browser that can't cope with the new Facebook design, so it instead shows you the old Facebook design (with the blue bar at the top.

After installing the add-on, if you have any already opened Facebook tabs/pages open, just reload them to see them change back to the old Facebook design / layout,

If Facebook has switched you over to the new design and you want out, never fear, Revert Site is here! Once Revert Site is installed Facebook will no longer be able to switch you back to the new site every 48 hours. They will only be able to switch you once they completely remove all the code for the old "classic" site, which may be months away from happening.