I reported this to support as well, but wondering if anyone else is seeing a similar issue:
Using the Bitwarden add-on with Firefox 72.0.1 on Fedora 31, editing existing sites seems to cause the pop-up window to auto-close under some circumstances:
after typing some characters in the Name field (the username field seems fine)
after selecting a folder (the drop-down menu is shown but the editing window is gone)
The add-on is last updated on December 27, and I don’t recall experiencing this issue until a couple of days ago - but I don’t edit my sites much so maybe it’s been there for a while.
I’m seeing something similar as well, also Firefox 72.0.1 on Fedora 31. In my case it seems to be triggered when a tooltip appears in the add-on pop-up, or when clicking on a drop-down menu. In the case of the drop-down, the main pop-up closes, but the drop-down list remains visible.