My library's OPAC website doesn't currently use HTTPS ... Trying to view it with a secure connection 'crashes' it regardless of browser. However once I accidentally tried to visit the site via HTTPS and now it automatically tries to server me the secure version no matter what I do. I've had the same problem in CHrome for a while, and while I can use the solution presented in this similar question and it will fix it for a little while by my next session the HTTP to HTTPS redirect is back in chrome. For that reason I've been using Firefox mostly until today when I accidentally pasted a HTTPS link to the website into firefox now firefox will only serve the HTTPS version as well.
Exit Firefox and edit the file
Delete the line with your domain in it. Then restart Firefox. That will stop the redirection. That file is like Chrome's
999 will be random letters and numbers. The path is for Windows. Use
Menu > Help > Troubleshooting Information > Profile Folder to find where your profile is located.
Confirmed Chloe answer!
In linux the file is in: