UI customization half-broken in Tor Browser 8.0a3

seen with Tor Browser 8.0a3-build1 on Linux (64 bit)

Changing the UI via the menu entry "Customize" does not work anymore because the customization view closes immediately after opening, so drag-and-drop is impossible. Right-clicking on a menu entry and selecting "Move to Toolbar" still works, as well as "Move to Menu" for something which was moved to the toolbar.

Maybe #25147 (moved) is the reason.

Trac:
Username: viktorj