I was able to open https://www.realtor.com/ just fine. So, the site should open fine in Firefox. I haven't come across that specific error before, so not sure what it could be. It probably try Firefox in Troubleshoot Mode ( Help -> Troubleshoot ) to see if the site will load then. That might point to an extension being the issue.

You can try these steps in case of issues with webpages: You can reload webpage(s) and bypass the cache to refresh possibly outdated or corrupted files. *hold down the Shift key and left-click the Reload button *press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux) *press "Command + Shift + R" (Mac) clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Settings). "Remove the Cookies" for websites that cause problems: *Settings -> Privacy & Security<br>Cookies and Site Data: "Manage Data" "Clear the Cache": *Settings -> Privacy & Security<br>Cookies and Site Data -> Clear Data -> [X] Cached Web Content -> Clear *https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox *https://support.mozilla.org/en-US/kb/how-clear-firefox-cache Start Firefox in <b>Troubleshoot Mode</b> to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if <b>hardware acceleration</b> or <b>userChrome.css</b> is causing the problem. *switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes *do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window *https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode *https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems *https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop *https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection *https://support.mozilla.org/en-US/kb/trackers-and-scripts-firefox-blocks-enhanced-track