Is Version 14.1.2 obsolete?

If the tool you're using doesn't work anymore then it's time to try another tool. Firefox is an excellent browser. I would not install Chrome, however, as that brings with it a lot of cruft that Google uses to track and identify you. If you want to use a Chrome-based browser then check out the open source alternatives like Vivaldi and Brave.

If some site does not work in Safari, go ahead and use Firefox or some other browser (I'd not use Chrome because it is a resource hog, though).

Finance sites and banking are an exception at least for me. For a while a relative used an old Mac with El Capitan and Firefox 78.15.0esr. But I advised to do banking via a newer iPad instead because if something goes wrong for whatever reason, the bank might wash its hands and blame the customer for the losses because an officially incompatible system was used.

You can run the current Firefox by downloading Firefox Dynasty (constantly being updated with build based on latest Firefox):

https://github.com/i3roly/firefox-dynasty ('Latest' download under 'Releases' lower right)

See also https://www.mozilla.org/en-US/firefox/all/desktop-esr/osx/en-US/ :

"Note: If you are using Windows 7, Windows 8, Windows 8.1, or macOS

10.12, 10.13 or 10.14, then please download ESR 115 in order to use

Firefox."