Firefox 68.0.1 (64-bit) language packs don't work right.

I'm having a problem with English language packs.
Linux Mint 19.2 installed Firefox with packs for
English Great Britain and English Canada. Since
I am in U.S. and some spellings are different I
installed English U.S. pack. The problem is the
builtin spellchecker still wants to use non-U.S.
spellings like "colour" and "labour" instead of
"color" and "labor." I don't get it. Both the
Great Britain packs and Canada packs are disabled
or they are supposed to be. I can't delete them
either because it's not an option that offered.
It's not a big deal but I've seen this problem
for a few years and it's annoying. Does anybody
have suggestions?