HI kinito_alc , That is what is expected. However if you would like to leave feedback for the developers you may submit feedback directly to the Advocacy team through the following page:

• Submit your Feedback

The User Advocacy team reviews all feedback and reports on the findings to the product teams and relevant parties, helping to influence and shape our products.

Thanks for the response, I'm marking it as answered.

yet I see it as unexpected result that tabs that were opened for several hours are closed when forgetting 5 min.

And thanks for the link to give feedback the dev team!

See also:

• https://support.mozilla.org/en-US/kb/forget-button-quickly-delete-your-browsing-history

The chosen answer is not what should be expected! To the layman, "forget the last 5 minutes" means that the browser returns to the exact point 5 minutes ago including the session data . It is not a feature; it's a bug!

I had exactly the same problem as the author. Luckily, I had refreshed Firefox (due to overabundance of addons) a few months ago, so I had a backup profile (with an old session). It didn't take long to restore the newer session. However, I don't think that backing up the profile once-in-a-while is the preferable solution.

Did you read all the text in the doorhanger that opens in you click the forget button?

The developers see this button as some kind of panic button (DOM id:#PanelUI-panicView) to erase what you have been doing and not as a simple forget action.

Proceeding will:
Close all Tabs and Windows
Delete Recent Cookies
Delete Recent History
Open a new clean Window
This action cannot be undone.

Indeed I did. It says nothing about the session, though. The relevant line to this case is "Open a new clean Window". However, it does not imply that the session will be erased, but rather that one would have an option to choose whether to continue with the previous session or start a fresh one.

It is good to know that the original intention of the developers was a panic button. Yet, the given name "Forget" and the tooltip description "Forget about some browsing history" are misleading. IMHO, "forget the last 5 minutes" should return to the exact session point of 5 minutes before. I believe that the original author of this thread understood this doorhanger text similarly.

As I see it, there is a confusion as for whether it is a "Forget" or a "Panic" button. These two viewpoints cannot coexist, and one must be chosen. If the "Forget" approach is selected, then the button behavior must be altered. Should the "Panic" approach remain, then the name of the button ought to be changed and the description must be clarified. For example, adding the following line to the doorhanger text:

       Clears Session and Session Data 

would have prevented any misinterpretations.

"Close all Tabs and Windows" implies that you lose the current session. "Open a new clean Window" implies that you create a new session because all tabs and windows have been closed.

Not quite. I can close all windows and tabs and return to my previous session. Moreover, I can also clear history and cache online or offline (e.g., with CCleaner), and still return to my session. Even when Firefox crashes (a rare occurrence), and opens a new clean window, it nevertheless asks whether I want to restore windows and tabs or not. The "Forget" button behavior should be consistent with that.

Clearing history does not clears session nor closing windows or opening new ones. Firefox manages sessions by its own, and quite well. I firmly believe that a button called "Forget" must not alter a session opened for more than a week.

Forget means really forget with no way to undo this action unless you have a backup that you can restore. This is the case with the Forget toolbar button and with "Forget About This Site" in the right-click context menu of an history item.