This issue can be caused by corrupted cookies or cookies that are blocked.

• check the permissions on the about:permissions page and in "Tools > Page Info > Permissions"
• https://support.mozilla.org/kb/fix-login-issues-on-websites-require-passwords

Clear the cache and remove cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

If clearing cookies didn't help then it is possible that the cookies.sqlite file that stores the cookies got corrupted.

• Rename (or delete) cookies.sqlite (cookies.sqlite.old) and delete other present cookies files like cookies.sqlite-journal in the Firefox profile folder in case the file cookies.sqlite got corrupted.

• http://kb.mozillazine.org/Cookies
• https://support.mozilla.org/kb/Deleting+cookies

Still not working. Any other ideas?

Some websites are sensitive to your network connection details and will require your password if they change. Sometimes this can be caused by the "Autodetect" proxy setting.

Could you check here:

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

The default of "Use system proxy settings" should piggyback on your IE/Windows "LAN" settings, but you also could try "No proxy" to see whether that makes any difference.

Also, to rule out other extensions as a possible culprit, could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

Starting in safe mode seemed to have temporarily resolved the issue, but I am unsure which extensions could be the problem. I have the following extensions:

• Internet Download Manager
• Adblock Plus 2.6.9
• Adblock Plus Pop-up Addon 0.9.2
• Classic Theme Restorer 1.3.1.1

None of these have caused any issue before.

The only one that seems remotely likely to be blocking website content is Adblock Plus, but I have not heard that it affects cookies. I think it has a feature to block it from affecting one particular website. If you try that, does it make any difference?

I have tried completely removing Adblock Plus, and it does not resolve the issue.

If you disable the other 3 extensions in "normal" mode (from the Add-ons page) does that resolve the issue? Safe Mode changes some other settings, so let's try that to see whether it actually is caused by extensions.

You can open the Add-ons page using either:

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

In the left column, click Extensions. Then on the right side you can disable all of them.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Any effect on the site's ability to keep you logged in?

Disabling the extensions does not help, so obviously it is something else. I tried it in safe mode for about 5-10 minutes and everything was fine. So far I have only noticed this issue on this one website.

It's really hard to think of how other things disabled in Firefox's Safe Mode could be affecting cookies. Those include:

• Hardware acceleration of graphics
• JavaScript compilers (to improve performance running large scripts)
• Certain appearance customizations (optional userChrome.css, userContent.css files)

It's fairly easy to disable hardware acceleration to test that:

"3-bar" menu button (or Tools menu) > Options > Advanced

On the "General" mini-tab, uncheck the box for "Use hardware acceleration when available"

This takes effect the next time you exit Firefox and start it up again. Any difference??

Disabling the compilers requires a visit to the about:config preferences editor. I haven't looked this up for a while, so hopefully another volunteer knows them off the top of her/his head.

You can also check that you do not run Firefox in permanent Private Browsing mode (Never remember history).

• https://support.mozilla.org/kb/Private+Browsing

• Tools > Options > Privacy > Firefox will: "Use custom settings for history"
• Deselect: [ ] "Always use Private Browsing mode"

You can check for problems with preferences.

Delete possible user.js and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in the current Firefox release.

• http://kb.mozillazine.org/Preferences_not_saved
• http://kb.mozillazine.org/Resetting_preferences

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History > Show All History" or "View > Sidebar > History") or via the about:permissions page.

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks, cookies, passwords, cache, history, and exceptions, so be cautious and if you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of the involved files.

It doesn't have any lasting effect, so if you revisit such a 'forgotten' website then data from that website will be saved once again.

No luck. I am now completely clueless as to what is causing this. This is the only site effected that I am aware of.

You can check if DOM Storage is enabled.

• http://kb.mozillazine.org/dom.storage.enabled

I have tried everything as well as a clean install. Does anyone else have any ideas? I have researched this until I am blue in the face. Any help is appreciated.

Create a new profile as a test to check if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

Issue resolved. It was my antivirus, ESET NOD32. I had to add Cheathappens to the allowed URL addresses under advanced settings. Never had this issue with ESET before, so I never thought of looking there. Thanks to everyone for the help.

You're welcome.

Thanks for reporting back on how you solved it.