I believe I mentioned this add-on last year when Mozilla unleashed Australia’s. Aris has put together an add-on which allows you to more than just customize, but rather fix the User Interface changes that Mozilla has made over the past year. Some of these includes:
- Disabling Pocket
- custom ‘about:newtab’ page for Firefox 42+ (developmental build)
- show add-on version number (version numbers will be removed starting with Firefox 40)
- Disable Reader Mode
- Options/Preferences in new window instead of new tab
There are many more customization options available. Before installing the add-on take a moment and read through the About this Add-on section to get an idea what you can do with this Add-on. Once installed go the Tools Menu in Firefox and select Classic Theme Restore to view all the options and starting fixing/customizing.