Turn Firefox into Edge browser. Microsoft Edge browser comes with two themes: Light and Dark. Light theme is enabled by default, you can choose and enable dark theme for Edge browser by visiting the Settings.
Firefox dev edition features a beautiful dark theme, you can activate it now for release and beta channels also through an add-on.
For nightly, see: How to Enable Firefox developer edition’s dark theme in Nightly:
Now if you like Edge dark theme and want to dress Firefox browser with that, you can, here is how.
UPDATE: Another add-on with name ‘Black Edge theme for Firefox‘ that doesn’t require Stylish to be installed is now available on Mozilla add-ons site (link), enjoy!.
Get Microsoft Edge’s dark theme for Firefox browser
1. Visit this page and download the rar file to your computer.
2. Extract the contents to a folder, open the ‘Main Theme’ folder and the text file in it, copy the entire text to clipboard.
3. Now open Firefox browser, install stylish add-on (requires a restart)
4. Click on the stylish icon on the navigation bar, Choose ‘Write new style’ > ‘Blank style’ and paste the text we’ve copied earlier
5. Give a name for the style like ‘Edge theme for Firefox’ or whatever you like, and click on ‘Save’ button.
6. See your Firefox browser now, it has turned into Edge.
To restore Firefox default theme or UI, visit ‘User Styles’ in Add-ons manger and disable or remove the style.
Customize Mode in Nightly now lets you Easily switch between Installed and Recommended Themes