Reproducible on: Firefox 46.0a1 and Firefox 45.0a2 across all platforms STR 1.Use '-no-remote -p' to start Firefox with two separate profiles, A and B. 2.Login on both profiles with the same Firefox account. 3.On profile A, ensure that at least “Tabs” sync option is checked in about:preferences#sync 4.Open a few tabs on profile A and go to Panel Menu -> Synced Tabs. 5.On profile B, having at least “Tabs” sync option checked, click on Panel Menu -> Synced Tabs ER The favicons are automatically displayed after Sync process. AR Firefox does not show the favicons until the page is visited. See screenshot: http://i.imgur.com/9wpYNgt.jpg Additional notes: - This issue is reproducible on Firefox 46.0a1(2016-01-11), Firefox 45.0a2 (2016-01-11) under Windows 10 64-bit, Ubuntu 14.04 64-bit and Mac OS X 10.10.5.