This issue should resolve itself after you perform these steps:
1) Close the Extinguisher window/tab
2) Clear your browser's cache and cookies
3) Completely close your browser
4) Reopen and attempt to log in again
After I waited a bit for my login to time out, I found the site worked normally again without going through any of the above. I replied to say so, but added:
Also, I've got to say as a longtime IT professional that advising a user to clear all cookies as a preliminary troubleshooting step is a nasty, nasty thing to do to a person. Suggesting they should search for and clear cookies specific to your site would be fine. Deleting ALL cookies will screw up SO MANY things for the average user that you will be wreaking considerable havoc that will cost them countless hours. You should avoid being that destructive at all costs until you are so deep into troubleshooting that it's clear nothing else could possibly work.