MinimizeToTray add-on keyboard shortcut reused by Xmarks

For users that have MinimizeToTray installed and find Ctrl-Shift-M (the MinimizeToTray keyboard shortcut) no longer minimises Firefox to the System Tray:

Disable Xmarks
Restart Firefox
Enable Xmarks
Restart Firefox

taDA! Ctrl-Shift-M now minimises Firefox to the System Tray and Xmarks works as you'd expect.

Background:

Having upgraded Xmarks I found that Ctrl-Shift-M caused a drop-down to appear beneath the Address bar with a line of text in it (didn't note what it was).

Ctrl-Shift-M appears to be the keyboard shortcut for Xmarks' "Get Site Info" Address Bar icon.

Disabling and enabling the Xmarks add-on appears (for whatever reason) to remove the keyboard shortcut from Xmarks (and thereby enable it to minimise Firefox to the System Tray).