Tabs Aside!
a simple and easy-to-use tab manager for Firefox, inspired by the Microsoft Edge feature Tabs Aside.
Run the source code
Go to about:debugging and click Load temporary Add-on and select manifest.json (located in the tabs aside root directory).
It is recommended not to use your main profile as development vesions might corrupt data. To create a new profile go to about:profiles.
If you have web-ext installed simply run web-ext run inside the tabs aside root directory.