I chose this keyboard shortcut a bit randomly. I’ll think about adding a better one instead of or in addition to the current one. Please tell if you have a suggestion.

Edit: (Ctrl+)(Shift+)F2 might be a good choice (Shift+F2 is used for developer toolbar which will be removed in Firefox 62).

Edit 2: The shortcut is now Ctrl+F2!

Edit 3: damn I missed the part where you said it doesn’t work by click. This is now fixed.