Here's another problem using PB is another fast way to loose all your tabs as well and this isn't a browser fault. PB should only be used for extreme cases-in my opinion. Everyday standard Browsing is what you should be using. And doing your PB will lead to problem should the browser closeout user caused or system caused. This way you can always restore sessions when you reopen a accidentally closed browser and have all your tabs back. But should you close the browser before reopening the sessions those tabs will also be gone.

Your response is opinionated and does not address the issue. By addressing PB you are only covering one aspect I mentioned and you are promoting personal preferences/opinions.

If you had taken a look at the bug I quoted it discusses at length that there are numerous cases where a restored session substantially differs from the closed one: timetable enquiry results are replaced by the entry form, or by a "session has expired, please re-enter your data" note when they were previously sitting in a tab no matter how long ago they were obtained, Startpage search results are replaced by the search form, and various dynamically created and modified content will look much different than before, some sites require you to login again and perform various navigation steps before showing the content you had previously obtained.

Also, even where the same content is restored, various pages will need to be re-loaded (depending on the server settings for client caching) using bandwidth, which is a nuisance on a metered mobile connection and a time waster when your connection is slow.

(Besides as a matter of fact including content from google.com is pretty much ubiquitous among the webpages I visit, so if I want to not present certain browsing activities to Google as part of the profiling they do on me, my best bet is to conduct them in PB -- whether Firefox still provides Google enough clues for fingerprinting my session without any cookies and correlating the PB with the regular session is open to speculation. Seeing that Firefox is marketing itself as a privacy browser, I would hope that they go to some length to minimize such clues.)

Fact is that bug 550559 was closed as tested and confirmed for FF 65, so as described in the bug, Firefox should now honour browser.showQuitWarning and browser.warnOnQuit (which I have and had set for a long time) and I ask why FF 66 does not!

Hello kede81,

Would you please take a look at this article :

https://www.ghacks.net/2018/11/27/mozilla-changes-firefoxs-warn-on-quit-logic/

Hi McCoy, thank for the hint. However, this describes the result of resolving bug 550559 which is the behaviour I expected in FF >= 65 but did not experience in FF 66. Apparently, a new setting browser.sessionstore.warnOnQuit was introduced and set to false by default, I found this mentioned in comment 223 of https://bugzilla.mozilla.org/show_bug.cgi?id=419009 and in https://www.reddit.com/r/firefox/comments/ajh9fo/firefox_does_not_warn_me_when_closing_a_private/ but I am puzzled why it is not mentioned in bug 550559 and how people who confirmed testing 550559 could know how to test without knowing this new parameter. 550559 made and still makes me understand that the pre-existing parameters browser.showQuitWarning and browser.warnOnQuit should govern the behaviour, or was I missing something in one of the comments, then feel free to point it out.

I have an experimental extension which you can try to prevent accidentally closing a private window:

https://addons.mozilla.org/firefox/addon/prevent-closing-window/

It has an annoying tendency to show its page more than once, but I need to spend more debugging time to sort that out.

It appears that

browser.warnOnQuit has a default value of true

in Firefox 66 (at least on Windows), and

browser.sessionstore.warnOnQuit has a default value of false

which is the traditional behavior of not warning if you have Firefox set to restore your session automatically. There is a new checkbox for that on the Preferences/Options page: