Version 1.0 works.

1.60 seems to not work with Waterfox 56.2.5 (I e-mailed the developer):

a) a click on the toolbar icon is non-effective

b) keyboard shortcut customisation is non-effective

– those two issues, plus conflict with a shortcut for a different extension, make 1.60 unusable for me.

Back to 1.0 for me …