Previously it was possible to assign a favicon to all of your bookmarks, but that favicon would only show up on a tab for exactly that URL. The moment you started browsing the bookmarked site, let's say example.com to example.com/whoops/, it reverted back to the original. At least that's how it was for me with 3 different add-ons.

Now, with this extension, most bookmarks don't accept custom favicons (which I know is due to Firefox's limitations), but they do show in tabs even when I browse the site. Subdomains need extra favicons.

It seems Firefox users sadly can't have custom favicons for both bookmarks and tabs. The way it is now, Favicon switcher does a great job.
One suggestion, though: Please enlarge the add-on window just a tiny bit. Right now, I have to hover over URLs to identify them. With 100+ custom favicons, that can get a bit tiresome.