These are some useful extensions that I use daily in my pretty heavily configured Firefox.

Appearance / Browser

Tree Style Tab

Firefox add-on / GitHub

Allows you to work with tabs as trees.

If you want to remove tabs from the toolbar, you’ll need to add some CSS to your userChrome.css file:

#TabsToolbar {
  visibility: collapse !important;
}

Adaptive Tab Bar Colour

Firefox add-on / GitHub

It basically just changes the Firefox theme to match the current website.

As you can see, it works well with Tree Style Tab.

Dark Reader

Firefox add-on / GitHub

This one is well-known. I use it at night when the website does not switch to a dark theme.

Miscellaneous

Price Perspective

Firefox add-on / Git

Helps you put prices in perspective by comparing it to other people’s income or your own.

Terms of Service; Didn’t Read

Firefox add-on / GitHub

Gives a grade and details over how bad the TOS of the current website are.

uBlock

Firefox add-on / GitHub

uBlock blocks a variety of stuff: ads, trackers, coin miners, popups, etc.

Vimium

Firefox add-on / GitHub

I only use one feature from this one: the goto word command. Allows you to click on stuff without touching your mouse.

Website-Specific Improvements

GitHub

Both these extensions add useful features on top of GitHub.

Enhanced GitHub

Firefox add-on / GitHub

Display repo size, size of each file, download link and option to copy file contents

Refined GitHub

Firefox add-on / GitHub

This one has too many for me to list, see the GitHub page.

YouTube

Clickbait Remover

Firefox add-on / GitHub

This extension replaces thumbnails with a frame from the video, effectively removing any clickbait while still showing a high quality thumbnail, so you can still get a good idea of what the video is about. It can also modify titles to stop partial or all caps titles.

Firefox add-on / GitHub

SponsorBlock lets you skip over sponsors, intros, outros, subscription reminders, and other annoying parts of YouTube videos. SponsorBlock is a crowdsourced browser extension that lets anyone submit the start and end times of sponsored segments and other segments of YouTube videos. Once one person submits this information, everyone else with this extension will skip over the sponsored segment.

Conclusion

That’s it for the extensions I currently use. :)