Hi Toulouse,
When you close FF and have a number of tabs open it should ask you if you want to either Save and Quit (this should restore your previous settings when you restart FF, or Quit.(If you select quit,when you restart FF it will load the site you have set as your homepage.)
Go into 'Tools,
Then 'Options'
Then open 'Main'. You will see 'When Firefox starts'.Select ,'Show my windows and tabs from last time'
Click 'ok'