SABnzb and Firefox

Having used Firefoxt to load SABnzb, for many years, and after updating Firefox to 83.0, I now get the following announcement
The following error was encountered while trying to retrieve the URL:

Connection to failed.
The system returned: (111) Connection refused
The remote host or network may be down. Please try the request again.
Your cache administrator is [root]

I have had to use Google Chrome, which I dislike immensely, to open SABnzb, with no problem whatsoever.

Any advie would be most welcome. Is it Firefox, or SABnzb? The latter I doubt very much, because it works in Chrome.

Still might be the App, if the developers were careless and idiotic enough to only care about Chrome compatability. Some think, everyone uses Chrome anyway, so that’s all you need to develop for.

There are many slight differences between Chrome and Firefox. E.g. some Google web apps and other Google products online are reduced in quality, when using plain old Firefox, without any special extensions. I don’t want to test it myself, because I have those extensions, but there was a time (maybe still is) that you could watch YouTube videos only up to 720p on Firefox, as opposed to having all resolutions at option in Google Chrome. This was done by Google on purpose to discredit Mozilla Firefox.

Google Chrome is also known to have much younger technologies enabled, which at first sounds very convenient, but at second thought this also means that Chrome may be much more insecure and instable, as the technologies they use are way too young. Firefox for example, tends to use more stable versions of those technologies, which in turn means, some features might not be available at the time when they are in Google Chrome.

Many yanks for the explanation, much of which, does answer so some of my questions i now understand the answers to; but I still have to find a “fix” for it, so again, any ideas would be most welcome. Have tried reinstalling both Firefox, and SAB but to no avail.