Lost my open tabs

Hi, I recently had to restart my computer and made sure that Firefox settings were 'open previous tabs on startup' before I shut down Firefox. I had about 30 tabs open, which were important and that I could not bookmark separately in time. After the restart, I opened Firefox to be shown a screen that said 'Your Firefox has been updated'. None of the tabs showed up, so I closed and reopened Firefox, but am just shown a blank tab. Please help, how can I restore my previous session with all the tabs? I really need help with it. Thanks Cameron