When a message is displayed, one can use 'load' events on the relevant DOM elements to carry out all sorts of manipulation. Ideally, one should be able to manipulate the message as a MIME structure read from file before it is even displayed or used otherwise, but this is currently impossible from an extension and extremely difficult even in the core code, as the code is old and highly problematic; see bug 248846. Still, it is necessary for an extension to be able to manipulate messages before they are printed, not only before they are displayed. So there should be some hook into the message printing process to allow that.
Product: Core → MailNews Core
Severity: normal → enhancement
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