In Google Docs, I cannot see the text in comments as it is written in black on very dark gray. The title of a document is also displayed strangely. Similar issues occur on other web pages.
The issues occur both when I use the standard Firefox appearance and with FT Deep Dark 14.0.
I use Firefox 44.0.2 on GNOME Shell 3.18.3 with the GTK+ theme
Adwaita-Dark-3.14-rev.2 on Arch Linux 4.4.1-2.
P.S.: I added a screenshot, I covered the user with a red box and removed the middle part of the image to fit the screen.