[orca-list] Orca moves unexpectedly on current page when opening new tab

[Alex ARNAUD <alexarnaud hypra fr>]

Hello all,

Environment:
- Debian "Stretch"
- Orca master
- Firefox ESR 60.4.0 with e10s enabled

I reproduce this for a while but I wasn't able to determine a scenario.

Steps to reproduce:
1) Open this page 
https://en.wikipedia.org/wiki/Amazon_(company)#Products_and_services
2) On the list of Amazon product and service move with down arrow until 
finding "Amazon drive"
3) Click with the middle button of your mouse or do contrl + enter on 
the link to open the link in a new tab
Note: I stay on the initial tab
4) When the new tab is loading move with down arrow (note: the issue not 
appears if I wait until the new tab was loaded)

Result:
Orca unexpectedly jumps back or jumps on another link

Expected result:
The loading of the new tab shouldn't move the caret on the current tab

Best regards,
Alex.