Tab Grouper por TheNamlessGuy

You can find a usage guide here.

Groups tabs in Firefox the same way you can do in chromium based browsers, replicated in the best way Firefox can currently manage.
The plugin allows you to group tabs together, and hide tabs that are not in the currently active group (if any).

The major thing it is missing from the chromium based browsers (at least in my opinion) is tab coloring. Unfortunately, Firefox doesn't really have a good way of doing this at the moment, as discussed here and here.
Once Firefox gets a good way of doing this, it'll be implemented.