This is generally a problem retaining the cookie the site sets when you enter the secondary form of authentication. Firefox's default setting is to keep a site's cookies as long as the site requests, but of course there are many ways to override this:

• Using a private window
• Changing Firefox's cookie settings
• Setting Firefox to clear history (if you include cookies) when it closes
• Manually clearing history (if you include cookies)
• Using add-ons that modify cookie handling
• External cleaning or privacy software that removes browser data

It's a lot of check, I know, but can you think of any recent changes?

To check built-in settings, you can start with this article: Websites say cookies are blocked - Unblock them.

One other possible reason for this is if your computer's IP address changed since the authentication cookie was set. To guard against using stolen cookies on a different computer, you may need to authenticate again.

One possible reason for an unstable IP address is using a VPN service, and another is a Firefox connection setting. You can check that setting here:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

Firefox 56-58: In the search box at the top of the page on the right side, type proxy and Firefox should filter to the "Settings" button, which you can click.

Firefox 38-55: In the left column, click Advanced. Then on the right side, with the "Network" mini-tab active, click the "Settings" button.

In All Versions: The default of "Use system proxy settings" piggybacks on your Windows/IE "LAN" setting. "Auto-detect" can lead to a flaky connection. You may want to try "No proxy".

Any difference?

A detail like a website remembering you (log you in automatically) is stored in a cookie.

You can use these steps to make a website recognize and remember you:

• you can create an "Allow" exception to keep specific cookies, especially in case of secure websites and when cookies expire when Firefox is closed.
• Options/Preferences -> Privacy & Security -> Cached Web Content: "Clear Now": Exceptions

In case you use "Clear history when Firefox closes" or otherwise clear history.

• do not clear the Cookies
• do not clear the Site Preferences

• Options/Preferences -> Privacy -> Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an "Allow" exception you may want to keep