The site could be temporarily unavailable or too busy. Try again in a few moments.
   If you are unable to load any pages, check your computer’s network connection.
   If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the web.

Have an app with a web interface that I used for years, but not with several of the latest versions of FF. Chrome, Edge, and DuckDuckGo all show the page as expected and the page functions properly. URL: http://127.0.0.1:8384/ Error looks like this: ---------- Unable to connect Firefox can’t establish a connection to the server at 127.0.0.1:[port number]. The site could be temporarily unavailable or too busy. Try again in a few moments. If you are unable to load any pages, check your computer’s network connection. If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the web. ---------- Have tried a large number of things including: Ping works for ip and hostname, v4 and v6 Confirmed address is accessible through other browsers Disabled extensions Added exceptions in Settings for HTTPS-only mode Various settings in about:config, careful to return them to previous states when they didn't fix the problem Tried Safe Mode (aka Troubleshoot Mode) Refreshed Firefox (as prompted before uninstalling) My last step is to reinstall, but thought I'd ask here first. Has anyone seen this before?