[vr46]

Not all of the ise/ize endings are interchangable, so the Firefox extension might be correct. -ize is only applicable for words with a Greek root, I believe, which is why choosing Oxford English was hardly a masterstroke on my part but it does make things more interesting.

I have little experience of Aspell short of seeing it pop up as a dependency now and then, but I will now try and attempt incorporating it into my Mac's dictionary, ideally it would work on iOS as well.

[MattBlissett]

The Firefox extension includes both versions, so I see a red underline for advertize (usage is archaic), but not for either realize or realise.

  aspell -d en_GB-ize-w_accents list < file-to-check

is the command to merely list spelling errors.