Hi, Nicolas,
Indeed, the spell check functionality in the forum compose window uses the personal spelling dictionary used in Firefox, the browser I use.
This of course does not at all explain why, only when in the forum software, I get this anomaly in the spell checker.
I realized that have not actually described that anomaly in this thread. It is this:
Sometimes, when there are two or more spelling errors (not yet corrected) in a paragraph, the wiggly red line indicating words with questionable spelling extends under the entire paragraph
Various things will clear this. Most often, if I delete any character in the paragraph (and I can then put it back), the phenomenon is cleared.
Sorry if I was snarky in responding to your first observation about this. I was just overcome by administrative foolishness on various other fronts!
Best regards,
Doug