Just a followup.
The browser based spell checker is working fine.
On this page now, if the spell checker comes up with a red line, a right click gives you the browser options for alternative spellings and also the option to 'Add to dictionary'.
When adding an FAQ (and presumably on other input) a right click actually throws up an osTicket generated menu instead.

which contains good things but not an 'Add' option - rather a nuisance.