Developer reply by Marco A.G.Pinto
Rated 1 out of 5 stars
I can download the dictionary, but there seems no way to install it.
This review is for a previous version of the add-on (3.1.8). This user has a previous review of this add-on.Heya, Dave,
Read the instructions here:
https://proofingtoolgui.org/en_installing.html
Basically, you can simply open the tools → add-ons → dictionaries, and drag'n'drop the .xpi file into this window.
To create your own collections, you must have a Mozilla Add-ons account.