[orca-list] Orca reads contents of non-active tab

[Alex ARNAUD <aarnaud hypra fr>]

Hello,

Environment:
- Debian 9 "Stretch"
- Firefox Nightly
- Orca master

1) Open this page: https://www.youtube.com/watch?v=QG6je87aQJQ
Let Youtube move to the next video automatically
2) Open a new tab with control + t and stay on the second tab
3) Wait until Youtube switches to the next video

Result:
Orca announce content from the Youtube tab whereas you're on another tab

Expected result:
I assume we shouldn't hear data from another tab.

Best regards,
Alex.