Bug 3606

Currently, if the PageDown or ArrowDown keys are used to scroll down an email, when the body message is reached, the cursor seems to go back to the beginning of the message. On the mailing list someone explained that this is because the cursor goes on to the attachments. However, this gives the impression that the cursor goes back to the beginning of the message. Whatever the case, this behavior is confusing to the user. 
The expected and desired behavior is that once the end of a message is reached, pressing the PageDown or ArrowDown keys should produce no effect.

I suggest implementing a "cursor stopper", which prevents the cursor focus from moving further ahead when the end of the body message is reached. In other words, if the end of the message is reached, and the user keeps pressing PageDown or ArrowDown, nothing should happen.