Question: Problem logging on

Recently I've run into a strange problem logging into the MaplePrimes site.  I have two computers, both running Debian linux.  On one, I can login in using the FireFox browser.  On the other I cannot.  It accepts the password, but immediately reopens the window that prompts for a password.  If, however, I switch to the chrome browser on that machine, I can then login.  Any idea why Firefox (aka IceWeasel, on Debian) would have an issue?  Have I configured something strangely?

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