Try checking to see if domain guessing suffix is enabled and disable it.

How to disable domain guessing: https://support.mozilla.org/en-US/kb/search-web-address-bar#w_turning-off-domain-guessing

Alternatively: Try launching Firefox in Safe Mode and see if the problem persists. It's possible that one of the extensions you're running might be causing problems. If launching in safe mode solves your problem, then follow the last link for help troubleshooting the issue.

How to start Firefox in Safe Mode: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode#w_how-to-start-firefox-in-safe-mode

How to test for faulty extensions: https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems#w_test-for-faulty-extensions

You may also have visited this domain in the past.

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History -> Show All History" or "View -> Sidebar -> History").

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks and history and cookies and passwords and cache and exceptions, so be cautious. If you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of involved files.

If you revisit a 'forgotten' website then data from that website will be saved once again.

• https://support.mozilla.org/en-US/kb/search-web-address-bar
• https://support.mozilla.org/en-US/kb/awesome-bar-search-firefox-bookmarks-history-tabs