How can we help you when you have provided nothing. No links to sites. No steps to replicate. No screenshots.

Not sure what you need. The sites in question, today, are bluemountain.com and dropbox.com. However, I had this problem a couple of days ago with another site but don't remember which. As you can see on the screenshot, the sign in just hangs there... However, when I go into private window, there is no problem. Thanks for any suggestions that you might be able to give me. claire

Smells like an add-on issue. Do you have the same issue with Firefox in Troubleshoot Mode?

I ass-u-me in Private mode you have no add-ons which is why it works.