Firefox Tips and Tricks
Firefox 57 will invalidate many of the existing useful extensions (like FaviconizeTab, which was a personal favorite). Some will see replacements. Others, however, can be replicated by existing customization options, albeit well-hidden ones.
In order for many of these tricks to be useful, you will need to create a file called userChrome.css. First, find your profile folder by going to about:support and clicking on Open Directory next to Profile Directory under Application Basics. Then, navigate to the chrome directory and copy the userChrome-example.css file to userChrome.css. Now open the file in your favorite text editor.
Reducing the width of your non-pinned tabs
Before Firefox 57, there were some addons that would reduce the size of your tabs (e.g. FaviconizeTab). If you want to replicate this, add this at the bottom of userChrome.css:
Hiding the close button on non-pinned tabs
With all the different ways to close tabs, from keyboard shortcuts to mouse shortcuts, who needs the close button to appear on the tab?
Hide back and forward buttons
If you have other ways of navigating the web and don't need to see the back and forward buttons (that is, they're just taking up valuable screen real estate), you can hide them like this:
Disabling Pocket completely
If you prefer to not use Pocket at all and wipe all traces of it from your browser, simply go to about:config and set extensions.pocket.enabled to false.