Great to have this, just wish there was an easy way to ensure my preferred dictionary was selected for all instances of Firefox all the time. (I understand that this is out of scope for this extension)

A lovely Aus word is missing from the dictionary. Please add fossick, fossicking, fossicked etc.

very nice, its just missing a few words:
transporter, gizmo, high(-)tech, pickup(s), sidecar, widescreen; to name a few.

Nice.
I use this both on ThunderBird & FireFox.
Trying not to be assimulated !!

Seems to use the Macquarie Dictionary, although oddly it treats the word "Macquarie" as an incorrectly spelled word. The homepage is down and this hasn't been updated in over a year, so that's why I only gave it four stars.