No such thing as Incognito mode. It is called Private Browsing https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history?redirectlocale=en-US&as=u&redirectslug=Private+Browsing&utm_source=inproduct

If want a truer private browsing then use Firefox Based Tor :

• https://www.torproject.org/index.html.en

Please let us know if this solved your issue or if need further assistance.

@Pkshadow Ok, I picked the Chrome's keyword for Private Browsing but the point remains same. In private browsing, Quantum shouldn't have saved the Gmail session but for some reason it is still doing that (checked again while typing reply). Isn't this against private browsing functionality?

P.S. - Don't want true private browsing, but don't want old websites/logins to continue either in private browsing mode.

Was the window exited or was it just shrunk to the bar. As to save the session and auto open to that is indeed strange.

To get rid of all old Netscape that maybe still hanging around from update after update. Please uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) DO MAC EQUIVALENT Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 57.0.4 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

Found out the issue, turns out one of the private browsing window was opened hence the session persisted. Once I closed all the private windows, the session got deleted. My bad.