I am using Firefox with the exact same plugins and settings in 3 different machines. Arch Linux, Windows and Ubuntu. In my fresh install of Ubuntu 16.04.1 Firefox won't keep me signed in to Sync no matter how many times I verify my account. Every time I open Firefox it prompts me to verify my account. I do it and less than a minute later I get a yellow exclamation mark that says that I need to verify again.
What could be the cause of this and how can I solve it?
I am using Firefox 49 and my system is up to date.