Firefox doesn't sync "background" tabs
Steps to reproduce: 1. open a bunch of tabs with middle-click (open on background) 2. click "sync now" on my laptop, wait until network traffic stops, and click "sync now" on desktop
Result: Not all the tabs from the laptop appear in the list of tabs from other computers. It seems like the list only contains tabs that I have actually viewed on the laptop, not that I have just opened on the background.
Expected result: All the tabs that I can see in my laptop's browser tab bar should be visible at the sync page on the desktop.