Remove firefox from unit tests for mysterious failures on ci

Author: robertbryer

test/unit/config/karma.unit.conf.cjs

@@ -118,7 +118,7 @@ module.exports = function (config) {
 
         // start these browsers
         // available browser launchers: https://npmjs.org/browse/keyword/karma-launcher
-        browsers: ['Chrome_for_docker', 'FirefoxHeadless'],
+        browsers: ['Chrome_for_docker'],
 
         // Continuous Integration mode
         // if true, Karma captures browsers, runs the tests and exits