As the previous thread was closed without actual resolution - https://support.mozilla.org/en-US/questions/941350?esab=a&s=&r=0&as=s I managed to solve this on my end by just reinstalling firefox using the localisation of the default dictionary language i wanted from here - http://www.mozilla.org/en-US/firefox/all/ A bit of a shame that the main download page doesnt select the geographically relevant localisation for you and even more so that changing the default language for the in built spell checker is so kak. oh well.