You can try these steps in case of issues with web pages:

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

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"

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

See also:

• https://support.mozilla.org/kb/fix-login-issues-on-websites-require-passwords

I had tried all that without success before posting here but I later learnt that this was a configuration issue and not a cookies or cache issue. I got solution on this site: http://f1compsolutions. forumstech.com/ t153-how-to-solve-paypal-one-moment-login-issue-in-firefox-browser . Though I donated 5$, the issue was permanently solved. Anyway I appreciate your replies.

broke link with spaces, Use tool at your own Risk!