Once upon a time, I debugged a web extension in Firefox by using the "Disable popup autohide" setting to facilitate inspection of its popup menu.

However, this setting is persistent across restarts and is active even when the devtools aren't opened. I didn't think to turn it off and the next time I used Firefox again, the popup behavior totally baffled me. It took me a bit of googling to realize what was happening.

Here are some references:

Quick solution:

  • Open about:config
  • Turn off ui.popup.disable_autohide