According to Firefox:
https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings
These items and settings will be removed:
Extensions and themes
Website permissions
Modified preferences
Added search engines
DOM storage
Security certificate and device settings
Download actions
Toolbar customizations
User styles (chrome subfolder containing userChrome and/or userContent CSS files, if previously created.)
In that case, how can I customize my User styles ?
