Our current context menu code predates contentEditable areas and confuses them with designMode. I've come up with some code that detects when we're really in a contentEditable area and doesn't force page spellcheck.
Created attachment 387839 [details] [diff] [review] Proposed patch
Test case in bug 433860
Comment on attachment 387839 [details] [diff] [review] Proposed patch Any reason for the // case "inherit": continue; left in?
Pushed changeset 5eafbc277e1c to comm-central.