As a Gnome Shell and a Firefox user, this is a must for my workspace. I just love when all my applications look a like and this addon is not only solves this issue of mine; It also provides extra space on your screen by removing the title and helps focus on the task.
It's always good to see people doing awesome things for GNU/Linux Community and widely-used applications like Firefox. I just love these little things.
A side note - Gnome 3.14 with Minimize and Maximize buttons enabled via Gnome Tweak Tool, does not affect Htitle unfortunately and leaves us with only ability to Close the Firefox, unlike Gnome 3.12. But I'm sure this is a known issue.
Keep the good work up Alexander!