Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

The problem persists when I am in Safe Mode.

To the best of my knowledge, Firefox does not come with a built in URL predictor. This is usually achieved with the installation of an addon. However, since the issue still occurs in safe mode, it is most likely no caused by an addon.

Can you please try the following:

1. Open the Firefox options
2. Go to the privacy settings
3. Locate the location bar section
4. Deselect "History" and "Open Tabs"
5. Select "Bookmarks"
6. Close the Firefox options
7. Restart Firefox

This will stop your history from being displayed as you type into the address bar. I believe that this may be the issue, as the faulty URLs are now stored in your browser history.

When I try it, the server is sending these headers:

Status Code: HTTP/1.1 301 Moved Permanently

Content-Length: 248 Content-Type: text/html; charset=iso-8859-1 Date: Thu, 10 Sep 2015 22:02:29 GMT Location: http://www.tessco.comhttps://tessco.com/ Server: Apache/2.2.26 (Red Hat Enterprise Web Server)

So there is an error in a server configuration file that will need to be fixed on the site. Most likely in a "rewrite" rule.

For now, best to put the www or if you see historical visits to the site in the address bar, to use one of the auto-complete options to get back to where you want to go.

Interesting, when I try it in Chrome, Chrome automatically adds www. first. If I put a full domain in the address bar (http://tessco.com) and try that, then I get the same bad redirect as Firefox does.

I am glad to hear that it's not just some weird issue on "my" firefox.

Just to let you know, this issue also occurs on my browser.