User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.4b) Gecko/20030507 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.4b) Gecko/20030507 Check Spelling is supposed to exist in: Preferences / Mail & News Groups / Composition. But doesn't. Nor while composing mail in any tool or menu. Reproducible: Always Steps to Reproduce: 1. 2. 3.
You must download a third-party spellchecker from http://spellchecker.mozdev.org. Please search the next time because this one is very easy to find in bugzilla ! *** This bug has been marked as a duplicate of 56301 ***