A year ago in other publication We explain how to disable title bar in Firefox, but those instructions are no longer valid for the current version of Deepin incorporating your new window manager dae-kwin, then we present the new method.
one-) Preferences install KDE by opening a terminal and run the following command:
sudo apt install systemsettings
two-) Open Firefox> Select the menu icon in the upper right part of the program (the menu icon has a form of three stripes)> Customize (or Customize)> on the bottom left, disable the "Title Bar option (or" title Bar ")
3-) Download the following rules file window "Firefox - Remove bar título.kwinrule"And save it to Desktop.
4-) KDE open Preferences (in the menu displayed after step 1).
5-) Go to Windows Management> Window Rules and give the Import button, select the file "Firefox - Remove bar título.kwinrule"And give the Apply button at the bottom of the window.
Usually that's it, now you'll have a Firefox without title bar. Below you can see screen shots before and after, also a video produced by our dear @Akibaillusion where you can see even better the end result.
WARNINGWhen performing the steps in this article can not be resized windows Firefox from the corners, to get it you must press ALT + F8