[orca-list] Can't reach the desktop when I'm in Thunderbird or Firefox

[Hermann <meinelisten onlinehome de>]

Hi,
the subject says it: When I start Firefox and/or Thunderbird I cannot
reach the desktop by pressing control+alt+d.
I've to perform the keystroke several times before the desktop appears.
In other apps there's no problem.
Perhaps something wrong with the Gecko script?
Pressing control+alt+tab or control+shift+alt+tab works reliable.
Hermann