Most of the times my saved tabs open, but every once in a while they don't and I lose them
I usually have a bunch of links open, so I have the settings set so my previous tabs always open. Most of the time, they do. Every once in a while, like today, though, Firefox decides to open to my home page instead. I never know when it is going to do this, so I never know which links to save in case it happens. Often, therefore, I lose several of the links I had open.
The Session Manager add-on may be helpful - it uses a more complete and fail-proof method, generally, and has a number of advanced features for session management.
Please let us know how above works out, and if we can be of further assistance. Detailed feedback is appreciated and helps us to help you better, plus enables us to better help other users with similar issues.