Rated 5 out of 5 stars

Could not do without it. So when it stopped working I was ready to try and fix it.
Until I realized the bug was likely linked to my firefox syncing of deprecated variables for the add-on.

What I had to do is go to about:config and set
spellchecker.detectDictionaryAsIType;true
Now it's responsive again and works as intended.
I saw in the reviews here that we have to set extensions.dictionary-switcher.autodetect;true
but I believe this is an old variable no longer used by the add-on and seems to have no effect on the add-on at all.

At any rate this is the most underrated add-on for firefox, hands down. :D

Props to developer/maintainer, even though it could have less bugs. Thanks a million.

This user has a previous review of this add-on.