Disable running Firefox from Karma on Macs (#5551)

The old admin UI is on its way out anyway, so it should be fine to close
#3894 with this. Karma is deprecated anyway, so if we want to fix it
properly, we would need to get a new (frontend) test runner in there,
which I don't see happening.

Note for reviewers: There are two commits here, which are best viewed
individually. The first just fixes some formatting issues in the Karma
config. Or you view the the changes with whitespace ignored, that should
also hide most (not all) of those "irrelevant" changes.

modules/admin-ui-frontend/test/karma.conf.js

@@ -1,3 +1,5 @@
+const os = require('os');
+
 module.exports = function (config) {
     config.set({
         basePath : './',
@@ -23,28 +25,38 @@ module.exports = function (config) {
             '../bower_components/angular-chart.js/dist/angular-chart.js',
             '../bower_components/angular-mocks/angular-mocks.js',
             // endbower
-      '../app/scripts/lib/chosen.jquery.js',
-      '../app/scripts/lib/angular-chosen.js',
-      '../app/scripts/lib/underscore-1.5.2.js',
-      '../app/scripts/lib/video-js/video.js',
-      '../app/scripts/lib/moment-with-locales.js',
+            '../app/scripts/lib/chosen.jquery.js',
+            '../app/scripts/lib/angular-chosen.js',
+            '../app/scripts/lib/underscore-1.5.2.js',
+            '../app/scripts/lib/video-js/video.js',
+            '../app/scripts/lib/moment-with-locales.js',
 
-      '../app/scripts/app.js',
-      '../app/scripts/shared/filters/filters.js',
-      '../app/scripts/shared/resources/resources.js',
-      '../app/scripts/shared/directives/directives.js',
-      '../app/scripts/shared/controllers/controllers.js',
-      '../app/scripts/shared/services/services.js',
-      '../app/scripts/modules/**/*.js',
-      '../app/scripts/shared/**/*.js',
-      '../app/**/*.html',
+            '../app/scripts/app.js',
+            '../app/scripts/shared/filters/filters.js',
+            '../app/scripts/shared/resources/resources.js',
+            '../app/scripts/shared/directives/directives.js',
+            '../app/scripts/shared/controllers/controllers.js',
+            '../app/scripts/shared/services/services.js',
+            '../app/scripts/modules/**/*.js',
+            '../app/scripts/shared/**/*.js',
+            '../app/**/*.html',
 
             'test/lib/jasmine-jquery.js',
             'test/lib/jquery-deparam.js',
 
             // fixtures
-      {pattern: '../resources/public/**/*.json', watched: true, served: true, included: false},
-      {pattern: 'app/GET/**/*', watched: true, served: true, included: false},
+            {
+                pattern: '../resources/public/**/*.json',
+                watched: true,
+                served: true,
+                included: false
+            },
+            {
+                pattern: 'app/GET/**/*',
+                watched: true,
+                served: true,
+                included: false
+            },
 
             'test/unit/setup.js',
             'test/unit/**/*Helper.js',
@@ -61,14 +73,20 @@ module.exports = function (config) {
             preferHeadless: true,
             // limit the list of browsers used by karma
             postDetection: (browsers) => {
-                const allowed = new Set(['ChromeHeadless', 'FirefoxHeadless'])
+                const allowed = ['Chrome'];
+                // Karma can't start FirefoxHeadless on Macs
+                // See https://github.com/opencast/opencast/issues/3894
+                if (os.platform() !== 'darwin') {
+                    allowed.push('Firefox');
+                }
+                const allowedSet = new Set(allowed.map(browser => browser + 'Headless'));
                 console.info('Detected browsers: ' + browsers);
-                browsers = browsers.filter(browser => allowed.has(browser));
+                browsers = browsers.filter(browser => allowedSet.has(browser));
                 console.info('Usable browsers: ' + browsers);
                 if (browsers.length < 1) {
-                    console.error("No browsers detected");
-                    console.error("Suggest installing Firefox or other FOSS browser");
-                    throw "No browsers detected";
+                    console.error('No browsers detected');
+                    console.error('Install one of ' + allowed.join(', '));
+                    throw 'No browsers detected';
                 }
                 return browsers;
             }
@@ -80,21 +98,21 @@ module.exports = function (config) {
         browserNoActivityTimeout : 60000, // by default 10000
 
         preprocessors: {
-      '../app/scripts/shared/**/*.js': ['coverage'],
-      '../app/scripts/modules/**/*.js': ['coverage'],
-      '../app/**/*.html': ['ng-html2js']
+            '../app/scripts/shared/**/*.js': ['coverage'],
+            '../app/scripts/modules/**/*.js': ['coverage'],
+            '../app/**/*.html': ['ng-html2js']
         },
 
         reporters: ['progress'],
 
         coverageReporter: {
             type : 'html',
-      dir : '../target/grunt/coverage/'
+            dir : '../target/grunt/coverage/'
         },
 
         ngHtml2JsPreprocessor: {
             cacheIdFromPath: function (filepath) {
-        var match = filepath.match(/.*app\/scripts\/(.*)/);
+                var match = filepath.match(/.*app\/scripts\/(.*)/);
                 if (match !== null) {
                     return match[1];
                 } else {