Rated 5 out of 5 stars

Nice try, but cannot install either the dictionary or language pack on TB 78 because, according to mozapps, the 'file appears to be corrupt'.

"If you can't install the language pack, it is a Mozilla issue."

Well, it's certainly a Mozilla product I'm trying to add it to, but that's the platform it's supposed to be built for. I didn't have any problem following the installation instructions from within TB and I d/led both the pack (the TB78 version) and the dictionary twice just in case.

Update: You are correct, Marco. It was a Thunderbird issue. I have reinstalled TB over the existing installation and add-ons now install and work fine. Thank you for your efforts.

This review is for a previous version of the add-on (3.0.1). 

If you can't install the language pack, it is a Mozilla issue.

My dictionary is a separated thing:
https://addons.thunderbird.net/addon/british-english-dictionary-2

Install instructions:
https://proofingtoolgui.org/en_installing.html