Steps to apply this config

• Create this preference in about:config page.

firefoxgx.left-sidebar

true

• We'll use the bookmark-bar to make the left-sidebar so, be careful to move first all the elements that you don't want in this bar to a new directory. The "bookmark-bar" should be in "always show".
• You should use "customize the toolbar" to move the extensions to the left-sidebar.
• You can use "flexible space" to create the separators in the left-sidebar and into the tabs-bar.

The social extensions used are:

PD: I'm the owner of Instagram Chat extension, Spotify extension and WhatsApp extension, The other extensions I used were for testing purposes.

Example of the layout of the interface before the apply of this config

Preview