Sounds like http://bugzilla.mozilla.org/show_bug.cgi?id=88164
Wolfgang wrote:
> When editing E-mail messages in Mozilla 0.92 the cursor hangs from
> time to time. It always happens at the end of a line, when I try to
> move the cursor backwards with the arrow keys (e.g. to correct a typo).
> The only solution is to use the mouse instaed of the keyboard and to
> click on on the position where I wish my cursor to be.
> This never happened with Mozilla 0.91 or earlier versions.
>
> If this is an already known issue SORRY! If not, please let me know if
> there are others out there having the same problem!
>
> Thanks,
> Wolfgang
>
