There is something called “Tab Groups” which i found cool.
It groups up your open tabs and lets you rearrange it. It also has a fancy name, called “Firefox Panorama”. You can bring it up simply by pressing Ctrl+Shift+E, or click the “Tab Groups” button in the tab bar.
If the “Tab Groups” buttons is missing, you can add it if you want, right-click on a toolbar and select Customize. You can then drag and drop the “Tab Groups” icon from the customize toolbar dialog onto the toolbars. You can use this method to add other icons to the toolbars.
See a video about it.