This extension does NOT WORK AT ALL when the profile folder is at different driver of firefox.(66.0b)
I always use the -profile in the shortcut to split the browser and the config apart.
For example, it works when Profile is in C:\ and failed when Profile in D:\ no matter the characters in the path(Browser is in C:\ in both case)
However, the job is really very well done I have to say, 2 stars is just to draw the attention and will changed after reply