Making sure the final add-on does not show in about:addons

docs/TESTPLAN.md

@@ -122,6 +122,12 @@ This study fires a survey at the following endings:
 * Verify that the study runs
 * Verify that no information is recorded and sent when private browsing mode is active
 
+**Not showing in `about:addons`**
+
+* Install the add-on as per above
+* Verify that the study runs
+* Verify that the study does not show up in `about:addons` (note: only signed study add-ons are hidden)
+
 **Correct branches and weights**
 
 * Make sure that the branches and weights in the add-on configuration ([../src/studySetup.js](../src/studySetup.js)) corresponds to the branch weights of the Experimenter entry. (Note that for practical reasons, the implementation uses 7 branches instead of the 5 defined study branches. The study branches that separate use different populations for training and validation corresponding to separate branches in the implementation)

src/manifest.json

@@ -3,6 +3,7 @@
   "description": "__MSG_extensionDescription__",
   "version": "2.0.0",
   "manifest_version": 2,
+  "hidden": true,
   "applications": {
     "gecko": {
       "id": "button-icon-preference@shield.mozilla.org",