new config.js, working in per user installation and with firefox 72+

[trupf]

The config.js as in this repo is not working if firefox is installed in the user account (instead of administrator). I'm not sure if it is working with current firefox (72+) at all even in standard installation as I can not test it. With attached config.js it will work again (and it should work for all installation no matter of operating system and installation path).

// 2020/01/12 config.js for loading global userChromeJS.js and users individual userChrome.js

try {

    const {
      classes: Cc,
      interfaces: Ci,
      utils: Cu
    } = Components;

    Cu.import('resource://gre/modules/Services.jsm');
    Cu.import('resource://gre/modules/osfile.jsm');

    function UserChrome_js() {
      Services.obs.addObserver(this, 'domwindowopened', false);
    };

    UserChrome_js.prototype = {
      observe: function (aSubject, aTopic, aData) {
          aSubject.addEventListener('load', this, true);
      },

      handleEvent: function (aEvent) {
        let document = aEvent.originalTarget;
        if (document.location && document.location.protocol == 'chrome:') {
		  // userChromeJS.js is just an option, the userspecific userChrome.js should be loaded anyway
		  try { let path = OS.Constants.Path.libDir;
            path = OS.Path.join(path, "userChromeJS.js");
            let uCJSFileURL = OS.Path.toFileURI(path);
		    Services.scriptloader.loadSubScript(uCJSFileURL, document.defaultView, 'UTF-8');
		  } catch(ex) {};
          let uCfile = Services.dirsvc.get('UChrm', Ci.nsIFile);
          uCfile.append('userChrome.js');
          let uCfileURL = Services.io.getProtocolHandler('file')
                        .QueryInterface(Ci.nsIFileProtocolHandler)
                        .getURLSpecFromFile(uCfile);
          Services.scriptloader.loadSubScript(uCfileURL, document.defaultView, 'UTF-8');
        }
      }
    };

    if (!Cc['@mozilla.org/xre/app-info;1'].getService(Ci.nsIXULRuntime).inSafeMode)
      new UserChrome_js();

    } catch(e) {};

 try {
    pref("toolkit.legacyUserProfileCustomizations.stylesheets", true);
} catch(e) {}