[orca-list] Thunderbird: orca repeats twice each lines when coming from Firefox on another workspace

[Alex ARNAUD <alexarnaud hypra fr>]

Hello all,

Environment:
- Debian 9 "Stretch"
- Thunderbird 60.5
- Firefox ESR 60.5.1 with e10s enabled
- Compiz as window manager on the Mate desktop
- Orca master

Steps to reproduce:
1) Open Firefox in workspace 1 on this page: https://l10n.gnome.org 
/vertimus/3134/154/100/ and place the caret inside the page, on a link 
for example
2) Open Thunderbird on workspace 3 and write a message (here in text 
mode and in a separate window)
3) Write multiple lines on the message
4) Go on the first workspace, here with the shortcut windows + 1 to 
switch on workspace 1
5) Switch on workspace 3 with a shortcut, here windows + 3
6) Press down arrow

Result:
Orca reads twice the line

Expected result:
Orca should read only one time each lines

You could find a debug log here:
https://framabin.org/p/?9ea76b194374b933#UvHwxyYUABnlrEuxJ2B8DSb+GIDifbK465vOOJJWBZM=

Orca has repeated the line:
"2) Open Thunderbird on workspace 3 and write a message (here in text "

Best regards,
Alex.