I've installed this Add-on, but Firefox still comes up with that strange American spelling.

It doesn't use English. I find that my spellcheck still uses the dumbed-down English that Americans use. And I can't remove the US English add-on.

I noticed that when I am writing in Firefox that that the word labled comes up as incorrect - with a red line under it (even though it is spelled correctly - in English [UK]) - and does not have a correction - if it is wrong (but it isn't). Why is this?

M.to boa obrgd