According to Thunderbird, the most widely used freeware email client, the word “occurance” is not a word, or at least it cannot detect that it is supposed to be spelled “occurrence.” I found it interesting that Firefox does not flag is as misspelled, yet Thunderbird does. Mozilla makes both of these products…you would think they would use the same dictionary. Hmm.

Isn’t it “occurence?”
Because if not I’ve been spelling it wrong for awhile.
Yeah, I guess Mozilla just doesn’t know it. I have actually run across a few other normal English words that it underlines as misspelled, yet MS Word and Google know perfectly. Hmm.
It’s spelled “occurrence.” I’m not sure why Firefox didn’t tell you it was misspelled; I found this page when I went to look up the word after I also spelled it “occurance” and I’m using Firefox.