Update: the shortcut can be configured in v1.4.0. Hope you like it!

Hopefully they will add support for customizing the shortcut in a future Firefox version. I can't do anything unfortunately. :(

You can always download the code, change the shortcut, and load the extension in about:debugging. :)

If you are interested in actually getting a solution to your problem, then please consider letting the Firefox developers know by posting here: https://bugzilla.mozilla.org/show_bug.cgi?id=1421811