This is a feature called "Domain Guessing", described here: https://support.mozilla.com/en-US/kb/search-web-address-bar#w_domain-guessing

You can turn it off by setting browser.fixup.alternate.enabled to false in about:config.

Firefox usually checks your local network first. By default, it asks Windows to determine whether myhotspot has an IP address, and Windows will check locally (or in the hosts file, if applicable).

However, if you are bypassing local network address resolution, for example, by using a proxy server or VPN, or by using an alternate DNS service provider other than Windows, then myhotspot will be undefined according to that server. In that case, fixup will be tried next.

To check on your Firefox connection settings:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the search box at the top of the page, type proxy and Firefox should filter to the "Settings" button, which you can click.

The default of "Use system proxy settings" piggybacks on your Windows/IE "LAN" setting. "Auto-detect" can lead to a flaky connection. You may want to try "No proxy".

Any difference?