Jun 14, 2018

Data loss or other problems can occur if the Firefox version you install is lower than the Firefox version you are currently using.

By default, different versions of Firefox will use the same user profile data. Data loss or other problems can occur if the Firefox version you install is lower than the Firefox version you are currently using. If you experience problems, try refreshing Firefox. See 

Refresh Firefox - reset add-ons and settings

 for details.