Session loss repeatedly

Hello! I’m a bit concerned because firefox has been functioning perfectly fine up to last week, when it started not crashing, but losing the opened sessions. I had many tabs that I would go back to after closing firefox. And then suddenly, when I opened it, there were no tabs at all. This happened again yesterday. And today again. I cannot find the option “restore previous session” like on the computer, so I go to history and manually restore the lost tabs, and of course it isn’t possible to remember everything, so lots are being lost. Could you help me? Many thanks!