There is an even easier solution to this, but it would have the consequence that you disable the session restore feature. Note: Firefox seems to clear those recovery options only when you close the browser, but not while it is still running (if you set it to 0). Then again, it may be time to create different user accounts for the different users on the computer to avoid this from happening in first place. If you share the browser, you may want to consider disabling the feature, as other users may use it to restore tabs that you have closed even if you have deleted the browsing history. If you find yourself in situations where you need to restore tabs exceeding the 10 tab limit that Firefox normally uses, or windows exceeding the 3 window limit, then you can increase that to adjust so that it fits better with how you use the browser. It is obviously possible to increase the values, which is fine if you are the sole user on the computer or if user profiles are used to distinguish between accounts.
