I noticed you have Firefox set to start up automatically in private browsing mode. Were you using that setting in your previous version of Firefox?

Could you test with Advanced SystemCare Surfing Protection disabled? You can adjust that on the Add-ons page. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. If this requires a restart to take effect, Firefox should display a link for that.

Also, could you check your connection setting here:

"3-bar" menu button (or Tools menu) > Options > Advanced > Network mini-tab > "Settings" button

The default setting is "Use system proxy settings" but try "No proxy" and see whether that helps.

I was going to say someone else posted this yesterday, but when I looked it up, it was you:

https://support.mozilla.org/questions/1014048

But let's continue here.

I did post the other day, but could never locate the question again.

Thanks for the suggestions. Neither worked.

Really aggravating when going through my emails and suddenly getting a session expired message. Thought initially (as per my original post) it was just yahoo email, but I found it affected other websites requiring a log in, too.

If you were NOT using private windows, I would suggest addressing possible corruption in your cookies database by renaming it and having Firefox build a new one. But I have no idea whether that is relevant to private mode (I don't know where the temporary cookie store is).

Looks like all I needed to do was to take it off private browsing. However, I have used that setting through who knows how many prior versions without a problem.

Thanks for your suggestions.

Do you have allow or block exceptions for cookies?

• Tools > Options > Privacy > "Use custom settings for history" > Cookies: Exceptions

In case you are using "Clear history when Firefox closes" and you want to preserve some cookies:

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

• Tools > Options > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings
• https://support.mozilla.org/kb/remove-recent-browsing-search-and-download-history

Note that clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, passwords, and other website specific data.

Clearing cookies will remove all specified (selected) cookies including cookies with an allow exception that you would like to keep.

You can create a cookie 'allow' exception to keep specific cookies, especially in case of secure websites and when cookies expire when Firefox is closed.

Another user is reporting a similar thing with automatic private browsing in Firefox 31: (Firefox is logging me out of websites).

One thought: you have your "third party cookie" setting set to Never. Previously, this was ignored in private mode, and all cookies were accepted for the duration of the session. To see whether that setting is an issue, could you try:

(1) With "Use custom settings for history" selected, change your third party cookie setting to Always and OK out of the dialog to save that change.

(2) Return to your "Never remember history" setting, restart Firefox, and test automatic private browsing again.

Any difference?

Since taking it off private browsing and using custom settings I have had no problems. Third party cookies is set to Never. History is set to clear when Firefox closes.

Even though there definitely remains some new issue with private browsing I consider the issue solved and do not need further assistance.

Thanks for everyone's suggestions.