Sooo I had tens of tabs open, with intention to keep them - I couldn't find an option to save all of them, so decided to update the app, just in case FF caught up with some functionalities I've seen in my other browsers - bookmarking all tabs, namely. After I've updated, all my open tabs are gone and "recently closed" is empty. There's no way to have the tabs back. I don't expect there's a way to solve this problem, but I'm posting it here just in case, and at the same time marking my segue to Safari.