Let’s say you’ve been using a custom made Firefox theme. You’re starting to get bored with it and would like to switch to back to the Firefox default theme.

Here’s how:

Go to the top of your browser and click Tools > Addons:

 

 

Locate the theme that you would like to switch to and click the “Use Theme” button:

 

 

Close the “Add-ons” window and restart your browser. When the browser re-opens, it will open with the new theme.

Follow the above process anytime you’d like to switch between any of your installed themes.