I left for edge. vertical tabs out of the box - check. ability to remove window title bar without editing css - check. ublock - check. sending tabs between pcs and mobile devices - check. (actually this one thing drove me away from ffx when it stopped working. about a year ago my android firefox(es) stopped syncing reliably. some devices synced, some synced occasionally, some never synced. related to the arbitrary limit on amount of bookmarks and tabs that could be synced, by ffx devs)