Pack refuses to load or work with new tabs

Pretty cool

How can this not be compatible with 82.0.2? Firefox keeps giving this feedback when I try to add it.

It is only giving me American English. Luckily, I can spell so I just use it for typos. Overall, as currently configured, it's not helpful for those who need it most

On ne sait pas si le module fonctionne ou pas! Rien n'indique!

This language pack claims to check English (GB), but it seems to have been written by an American.
Far too many spelling issues that prefer the American spelling to the proper British spelling.
If I had wanted American spelling, I would have opted to install the English (US) Language Pack instead.
Silly.

I have tried on about 3 occasions to change the default language of Firefox from US to UK English. It has never stuck, so the spelling corrections I make when marking student's work are shown as errors.
How can I ensure that the language setting NEVER reverts to US spelling?

(US) English default, is NOT the correct UK English dictionary.