Can no longer OPEN FACEBOOK and several other programs that were working fine until 3 days ago

macOS Mojave is outdated and no longer supported. The Safari browser that was installed with it is also now unsupported and lacks the security enhancements required by many newer websites.

If you are having trouble connecting to and using websites with your older version of Safari, try it with a newer third party browser that is still being updated to meet current internet security protocols.

I suggest you take a look at Firefox browser or Brave browser, though I'm not certain either of them will run in that vintage OS. Firefox ESR browser for older Mac OS.

Download an alternative browser and install it into your Applications folder. Launch and use that when you encounter websites that don't play well with Safari.

And, imho, you would do well to consider buying a newer Mac - less than 5 years old - that can run a more current, still supported, version of macOS.