Comment 13 for bug 1721614

This is still an issue in 18.04 and can be reproduced from the live image.

Steps to reproduce:
0. Use a laptop with high resolution display (eg. 3200 x 1800).
1. Boot from live image with external monitor plugged in.
2. Launch Firefox and enable the bookmarks toolbar.
3. Open and close the first item in the toolbar (or any other menu actually) => no problem.
4. Open the display configuration app and change config, eg. change scale from 200% to 100%, or change built in display's resolution to 1900 x 1080.
5. Open the first item in Firefox's bookmarks toolbar => it usually appears at wrong location. If not, try disconnecting the external monitor and opening the menu. At some point it will appear at the wrong location.