In my case, both contextmenu and stored credential dropdown list are miss-aligned (by approximately {-130px;-60px}) when the 'Title bar' display option is unchecked (=title bar not rendered).
When re-enabling 'Title bar' display, all miss-alignment are gone.
Kind of confirmation.
* Ubuntu 18.04.4 LTS
* 4.15.0-76-generic #86-Ubuntu SMP
* Xubuntu flavor
* Xfce 4.12
* Firefox 72.0.2
In my case, both contextmenu and stored credential dropdown list are miss-aligned (by approximately {-130px;-60px}) when the 'Title bar' display option is unchecked (=title bar not rendered).
When re-enabling 'Title bar' display, all miss-alignment are gone.