[Affected versions]: - 63.0, 64.0b4(x64, x86), 65.0a1 (2018-10-29) [Affected platforms]: - Win 10x64, Win 7x64, Ubuntu 16.04 [Steps to reproduce]: 1. Launch Firefox; 2. Resize the browser so it's not fullscreen; 3. Open any dropdown (page actions, OpenMenu, Pocket, Customize DevTools); 4. Press the F11 key; 5. optional: press F11 key again; [Expected result]: - menu is following the parent button [Actual result]: - WinOS: menus remain in place, jump on the next screen if multiple; - UbuntuOS: after step 5 the 3line/hamburger menu is open in another position; [Regression range]: - 1412364 seems to be at fault; [Additional notes]: - link for the issue: https://drive.google.com/open?id=1Df5HKwshYGPogcpPzehzLP_fN3rHE3DA - macOS was not added since the menus seem to be reopen properly, but they do remain displayed for about a second to much in the current position;

Hey Sam, mind taking a look at this? Thank you!

OK yeah it makes sense this is fallout from bug 1412364. I would prefer to fix this by closing the menu when we go to fullscreen. I don't see a compelling reason to support moving the open menu while we animate to fullscreen. :shorlander do you have an opinion or can you forward?

It's a nice behavior to move the menu and keep it open, but I would say that the menu closing would also be an acceptable behavior. Marking P5 due to low chance of users doing this.