To reply to another user. This addon gets intalled automatically, and it's visible when you right click in a text area (when you write text) >language>English (United Kingdom) and it allows you to make a spell checking in your text area. If you don't know how to use a dictionary in Firefox, please don't insult the dev, thanks. By the way, I'm looking for an English dic with all the local variants, US, Autralian, British, etc...
The only English dictionary I know of with the local variants is for LibreOffice and OpenOffice (yes, I am the guy who packs the extension for them).
My GB speller also has places from New Zealand, Australia and US.
It is used by other countries such as New Zealand.
A friend (I can't remember if he is from Australia or Canada) told me that the difference there is that they prefer -ize or -ise (can't remember) and since my speller uses -ize and -ise, I believe more than one country can use it.