Rated 4 out of 5 stars

This is not working when using Ambiance/Radiance themes with Gnome Shell (these are the themes from Ubuntu unity)
Do you know if there is any way to fix that ? The titlebar disappear when using F11 but not when using gnome full screen...

This review is for a previous version of the add-on (2.11.1-signed.1-signed). 

HTitle works like gtk-window-set-hide-titlebar-when-maximized method in GTK3 [1] by default. And your problem looks very strange.

Does Evince hide title bar on your system? And how HTitle works with enabled "legacy-mode" checkbox? And your Ambiance theme is theme for GTK or Mutter (windows manager)?

1: https://developer.gnome.org/gtk3/stable/GtkWindow.html#gtk-window-set-hide-titlebar-when-maximized