Same here with FF 70.0.1 in Windows 10, and yes, "Title bar" in checked in FF/Customize and no add-on installed except adblocker. Resizing the FF window or hovering over the minimize/maximize/exit buttons will turn the title bar (and probably window frame, which I don't have in my theme) transparent. Switching to another tab in FF will restore it.
Thanks for the replies. I'll give the "newest version install" a try and if that doesn't sort it I'll just shut off the auto update check. Anyway a minor issue but thanks all the same!
So, first of all, I'm very happy with WindowBlinds and haven't had any issues with the actual functionality of the application. One thing I have noticed though is that every time WindowBlinds checks for updates it seems to always hit a positive. For example I had an automatic update check yesterday and all of the files before and after the update are exactly the same size, same version, etc. While this can be resolved (sort of) by simply switching off "Automatically check for updates