Rated 5 out of 5 stars
by Aleksandr Seleznev (Developer) on October 24, 2017 · permalink
Web Extension API doesn't provide any way to hide titlebar. You can try to use external process via Native Messaging API, but it isn't good solution (a very bad hack actually) and will have complicated installation instruction. I have no plan to make it.
Mozilla Firefox will have native support for CSD soon (not sure that it will be shipped in Fx 57). You can track progress in https://bugzilla.mozilla.org/show_bug.cgi?id=1283299 and help with testing for example.
Sorry for starting another post but there isn't a reply option so i just wanted to thank you for taking the time to explain that the new Firefox CSD will resolve this issue in later releases , It looks awesome. :)
Here is a Link of how it looks if anyone is interested.