Browsing normally, tabs on the left. Switch to a different application and come back to Firefox and the tabs are at the top. It's happened twice so far and both times were fairly close to after I logged into a laptop that had been suspended/sleeping.
Macbook Pro running ElCapitan (screen shot is from here)
Dell XPS 13 running Linux Mint 17.3
Browsing normally, tabs on the left. Switch to a different application and come back to Firefox and the tabs are at the top. It's happened twice so far and both times were fairly close to after I logged into a laptop that had been suspended/sleeping. Macbook Pro running ElCapitan (screen shot is from here) Dell XPS 13 running Linux Mint 17.3