URL: https://jenkins.qa.ubuntu.com/login?from=%2F
Problem type: Site is not usable
Description: Login is not possible anymore with latest Nightly on Jenkins servers.
Steps to Reproduce 1. Open a Jenkins webpage (I'm using an internal one, but https://jenkins.qa.ubuntu.com/ shows the same issue)
2. Try to login (arbitrary username & password is OK)
3. Hit Enter or click the login button. Nothing happens with latest version of Nightly.

Browser / Version: Firefox 56.0 (2017-07-10)
Operating System: Windows 10
Tested Another Browser: Yes

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