I had cookies enabled & JS for userstyles.org allowed. When I logged in on main page (not the forum page), it took it & I could access my acct, etc. But when I switched to forums, it thought I wasn't logged in. I went through this a couple times. I had tried clearing cookies & caches & starting over - didn't help.
Finally I believe I logged in, starting from the forums. It took the login, but (I believe) it still gave the "howdy stranger" message. Again, cookies were allowed & so was userstyles.org scripts. I reloaded the page w/o doing anything else & suddenly it showed I was logged in - in the forums.
This took quite a while. I'm not sure what other, if any, 3rd party scripts are required to successfully login & move around the site (& stay logged in).