Same problem here. It also happens in Thunderbird.
Furthermore, when the popup menus don't work, also drag-and-drop doesn't work anymore. So tabs cannot be reordered, etc.
The bug appears almost always in less than 15 minutes when I'm using Firefox or Thunderbird. I never hide any toolbar, so indeed there also must be some other reason.
Same problem here. It also happens in Thunderbird.
Furthermore, when the popup menus don't work, also drag-and-drop doesn't work anymore. So tabs cannot be reordered, etc.
The bug appears almost always in less than 15 minutes when I'm using Firefox or Thunderbird. I never hide any toolbar, so indeed there also must be some other reason.