Using nightly as default target for npm start and functional tests

package.json

@@ -88,7 +88,7 @@
     "sign": "echo 'TBD, see: https://bugzilla.mozilla.org/show_bug.cgi?id=1407757'",
     "start": "web-ext run --no-reload",
     "test": "npm-run-all -n test:unit test:func",
-    "test:func": "FIREFOX_BINARY=${FIREFOX_BINARY:-firefoxdeveloperedition} ADDON_ZIP=./dist/button_icon_preference_-_shield_study_example-2.0.0.zip mocha test/functional/ --bail",
+    "test:func": "FIREFOX_BINARY=${FIREFOX_BINARY:-nightly} ADDON_ZIP=./dist/button_icon_preference_-_shield_study_example-2.0.0.zip mocha test/functional/ --bail",
     "test:unit": "NODE_ENV=test karma start",
     "watch": "web-ext run"
   }

web-ext-config.js

@@ -10,7 +10,7 @@ const defaultConfig = {
     overwriteDest: true,
   },
   run: {
-    firefox: process.env.FIREFOX_BINARY || "firefoxdeveloperedition",
+    firefox: process.env.FIREFOX_BINARY || "nightly",
     browserConsole: true,
     startUrl: ["about:debugging"],
     pref: ["shieldStudy.logLevel=All"],