Steps to reproduce
- Open Proton app menu.
- Try to open the "Send tab to device" sub-menu.
The Proton app menu should stay open and then slide to reveal the "Send tab to device" sub-menu.
This week I've twice now I've tried to open the Proton app menu and then all of the menu except the top edge disappears (possibly related to the FxA Sync animation spinning in the app menu?). See the attached screenshot.
Once the app menu disappears, closing and opening the app menu only ever shows the top edge until I restart Firefox. The Firefox Account toolbar button's menu can still open and show its the "Send tab to device" sub-menu correctly.