I can't login using Firefox on Linux Mint 17.3 MATE. I get as far as the captcha, answer it, receive a green tick confirming I'm not a robot, but once I click the LOGIN button I'm back to empty login fields and can repeat the process. Restarting Firefox in Safe Mode via Firefox/Help/"restart with Add-ons Disabled ..." doesn't solve the problem. Enabling all Cookies in Firefox (including third party ones) doesn't help either.
This is the second machine where I've had this problem. The other was my laptop running Linux Mint 17.2 MATE.
Logging in does work on both machines using Firefox in a virtual machine (VMWare) running Win10.
Any suggestions, anyone?