I used sidebery and edited the userchrome.css using guides from r/FirefoxCSS

here's some guides for them:

• https://www.reddit.com/r/FirefoxCSS/comments/rmi8dg/yet_another_sidebery_setup/
• https://superuser.com/questions/1268732/how-to-hide-tab-bar-tabstrip-in-firefox-57-quantum

But for reference, here are the codes for them (since Reddit appears to be down at the time of this writing)

userChrome.css

Sidebery Stylesheet

Here's the sidebery link on github

https://github.com/mbnuqw/sidebery

Note, to find your firefox profile folder:

https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data#w_how-do-i-find-my-profile