Comment 39 for bug 236901

This issue is a big concern when you have selected to "clear private data on exit", and selecting that option makes session support 100% useless. The issue with this feature is that it works differently if you are using it "on exit", or via menu option/hotkey.

The scenario for using the hotkey is this (in this scenario, the user has "browsing history" enabled as one of the items that will be cleared):
1. User is browsing sensitive material
2. User presses the hotkey to clear data.
Result:
All private data is cleared, but the tabs that are currently open are not closed, which leaves the "current" page in the history.

However, when using "clear on exit", all of the history is cleared, including the "current" item in the history, which leaves nothing to be restored on the next startup.

If a user is concerned with clearing their tabs when they close the browser, there is already an option for this where they don't enable session support in the first place. They can start the browser with their homepage or a blank page, instead of "Show my windows and tabs from last time". That is how it should be taken care of if a user wishes to disable session support.