A core difference between Firefox’s and Chrome’s private browsing mode

Most modern browsers ship with a private browsing mode that can be started independently from the main browsing session. It prevents the recording of history information in the browser so that information about the private browsing session cannot be retrieved once the window has been closed.

While it is certainly possible to achieve the same goal manually without that mode, for instance by clearing the history, cookies and cache files selectively to erase traces, it is comfortable to use and not as time-consuming.

All private browsing modes work in a similar way. They spawn in a new browser window which is independent from the main session. Users can open tabs in the window and access as many sites as they want.

There is however a difference between how Firefox's private browsing and Chrome's incognito mode function.

If you are using Chrome's incognito mode, you may have noticed that you cannot restore a closed tab in that mode. Not every user requires that functionality but if you happen to use the mode a lot, you may have encountered situations where you closed a tab only to come to a point later on where you needed to re-open it in the browser.

That's not possible however and if you cannot remember the address or the site you opened it from, you are out of luck and cannot open it again.

And Firefox? Firefox handles private browsing windows as their own instances. This means that you can re-open closed tabs when you are using Firefox's private browsing mode. To do so either use Ctrl-Shift-t or right-click on the tab bar and select the undo close tab option from the context menu.

Side note: Opera handles this the same way as Google Chrome, likely because it is also based on Chromium, while Microsoft's Internet Explorer the same way as Firefox.

You may wonder why the implementation differs when it comes to the undoing of tabs in private browsing. There does not appear to be an official answer for that but the most likely explanation is that Firefox and Internet Explorer handle the information on the window level while Chromium-based browsers on a tab level instead.