CTRL + SHIFT + Left and CTRL + SHIFT + Right shortkeys are working, but CTRL + SHIFT + 1 and CTRL + SHIFT + 9 are not working. Instead, the builtin CTRL + 1 and CTRL + 9 shortkeys are triggered.
Even after restarting Firefox... I'm using Firefox 54.0.1 64-bit and 58.0.2 64-bit, I get the same behavior on the 2.

"Move Tabs" uses four key-combos rather than buttons, and it moves only the selected tab. Two of the combos move the selected tab one place to the left or right, which my mouse cursor can do. Of the other two, Shift+Ctrl+1, or "Move The Tab All The Way To The Left," activates a different add-on (Nimbus Screen Capture) on my PC. There's no option to change the combo, nor one to select multiple tabs and move them all with a click.

The fourth combo, Shift+Ctrl+9, or "Move The Tab All The Way To The Right," works just fine.