There is a certain irony to using Sxipper to manage authentication to the SAML.xml.org site.
It took me a while to get it to work. Sometime ago I had turned off Firefox's Password Manager (but not cleaned out already saved data). After than, I installed Sxipper and it worked quite happily with the existing store of account names passwords. SAML.xml.org was the first site I've created a new account at subsequent to turning off the Firefox feature so Sxipper was understandably lost.