chore: remove firefox from base test browsers

.travis.yml

@@ -5,7 +5,6 @@ node_js: stable
 
 addons:
   chrome: stable
-  firefox: latest
 
 notifications:
   email: false

karma.conf.js

@@ -86,9 +86,7 @@ module.exports = config => {
   config.set({
     frameworks: ["jasmine"],
     reporters,
-    browsers: IS_SAUCE_LABS
-      ? Object.keys(customLaunchers)
-      : ["ChromeHeadless", "FirefoxHeadless"],
+    browsers: IS_SAUCE_LABS ? Object.keys(customLaunchers) : ["ChromeHeadless"],
     files: [
       "node_modules/@webcomponents/webcomponentsjs/webcomponents-bundle.js",
       "test/runner.js",

package.json

@@ -24,10 +24,10 @@
     "functional"
   ],
   "scripts": {
-    "dev": "karma start --browsers ChromeHeadless",
+    "dev": "karma start",
     "dev:coverage": "rm -rf ./coverage && NODE_ENV=coverage npm run dev",
     "test": "karma start --single-run",
-    "test:coverage": "rm -rf ./coverage && NODE_ENV=coverage npm run test -- --browsers ChromeHeadless",
+    "test:coverage": "rm -rf ./coverage && NODE_ENV=coverage npm run test",
     "coveralls": "npm run test:coverage && cat ./coverage/lcov.info | coveralls",
     "build": "npm run build:lib && npm run build:esm && npm run build:dist",
     "build:lib": "rm -rf ./lib && NODE_ENV=cjs babel ./src -d ./lib -s inline",
@@ -53,9 +53,7 @@
     "karma": "^4.4.1",
     "karma-chrome-launcher": "^3.1.0",
     "karma-coverage": "^2.0.2",
-    "karma-firefox-launcher": "^1.3.0",
     "karma-jasmine": "^3.1.1",
-    "karma-safari-launcher": "^1.0.0",
     "karma-sauce-launcher": "^2.0.2",
     "karma-sourcemap-loader": "^0.3.7",
     "karma-webpack": "^4.0.2",