Hi, thanks for your review. This addon isn't and never was a British English spellchecker as you seem to have thought, but for Oxford spelling, a variant of British English which uses -ize endings instead of -ise. You will notice that it does recommend spellings like 'travelled' over 'traveled' and 'manoeuvre' over 'maneuver'. It also should be noted that the suffix ‑ize has been in use in the UK since the 15th century, and only in recent years, with the rise of -ise spellings, has come to be seen as an Americanism.

Please see this Wikipedia article for more information: https://en.wikipedia.org/wiki/Oxford_spelling

For a British English spellchecker, I recommend this one: https://addons.mozilla.org/en-US/firefox/addon/british-english-dictionary-2/