Morning!
I believe I have managed to pinpoint the problem! I started from the top, disabling every single FF setting, one at a time, then removed all caches, restarted Win 7/64-bit and logged in to discuss.pixls.us again after each change.
The culprit turned out to be Security | Block reported web forgeries.
- When unticked, login just took about two seconds.
- When ticked, login needs about 19 seconds (but if you just logout and login again, login is fast).
This gave me ammunition for a Google search, and it seems to be a semi-known Mozilla bug: 1153674 - Website are loading/connecting slow and here is a quote from the comments there: When I disable “Block reported attack sites” and “Block reported web forgeries” in Options/Security, everything works normally. (Everything goes a lot faster on other sites to.)
The same behaviour occurs in Ubuntu 15.10/FF and Ubuntu 16.04/FF.
Actually, I do not believe that pixls.us is a “reported web forgeri”, I believe there is something else behind…