When you use PB mode then all session data is kept in memory and no session data (disk cache, cookies, storage) is saved to the profile folder although you can save new bookmarks and save passwords and save exceptions. All cookies will be session cookies that expire automatically, so websites can't store persistent data.

With "Clear history when Firefox closes" you can only clear some specific data similar to "Clear Recent History". There is also a Forget (panic) button available in the Customize palette. From the perspective of a website there is not much difference although a website can try to run JavaScript that doesn't work in PB mode to detect PB.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox
• https://support.mozilla.org/en-US/kb/forget-button-quickly-delete-your-browsing-history
• https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history

For comparison, what is the difference between cleaning up really well after a party at my house, versus having the party at someone else's house? When the party is at someone else's house, at no time does my house show any evidence that I'm partying.

thanks guys for the quick responses.....appreciated.