Some Firefox dialogs do not have title bar

[rocco.xyz]

Since I updated to Windows 10 I noticed that the DOM Inspector window and the FindBar Tweak window "Find in All Tabs" do not have a title bar (in Windows 8.1 they were fine), so I can not move or minimize them, I can close them with the Esc key.
Is it a Windows 10 problem, does someone else have the same problem?
These are windows of the XUL interface, right? Is it because XUL "has been deprecated"? (everyone talks about it lately)
How can I solve this problem?
I already tried to uninstall them and reinstall them, but it did not work.




Windows 10 Fall Creators x64 (I updated it today, but the problem was already before)
Firefox 55.0.3 x64 (the same version I used in Windows 8.1)
FindBar Tweak 2.1.12
DOM Inspector 2.0.16.1

[dickvl]

Is the window title bar enabled in Firefox if you check this in the customization mode window?

Can you open the system menu of these windows via Alt+Space?

[rocco.xyz]

Yes, "Title bar" checkbox is checked in the customization mode and "browser.tabs.drawInTitlebar" is set it to "false" in "about:config", and yes the standard context menu appears when I press the Alt+Space keys.