entering character sometimes creates spurious newline in firefox

[johnsdaniels]

On Firefox 8 on Windows 7:

steps to reproduce:

1. go to demo page
2. edit source and change it to "<p></p>"
3. stop editing source
4. focus on editor using the tab key (do not click on the editor)
5. type a single character

Expected: Just the character should be typed.

Actual: A newline spontaneously appears before the character, moving the character down.

[Jakub Ś]

Issue has been reproducible from CKEditor 3.3 on Firefox v4-9 browsers (It works fine in Firefox 3.6).