Fix firefox addon_success needle

I updated this last month without looking closely enough; one of
the matches was bogus. We now don't seem to get the 'added to
Firefox' popup any more, so we can't match on it, but I guess we
can match on the 'remove' button as an indicator that the add
worked.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

needles/firefox/addon_success-20200116.json

@@ -1,22 +1,22 @@
-{
-  "area": [
-    {
-      "ypos": 705,
-      "width": 32,
-      "type": "match",
-      "height": 34,
-      "xpos": 58
-    },
-    {
-      "width": 20,
-      "ypos": 71,
-      "xpos": 953,
-      "height": 19,
-      "type": "match"
-    }
-  ],
-  "properties": [],
-  "tags": [
-    "firefox_addon_success"
-  ]
+{
+    "area": [
+        {
+            "height": 15,
+            "type": "match",
+            "width": 15,
+            "xpos": 504,
+            "ypos": 500
+        },
+        {
+            "height": 19,
+            "type": "match",
+            "width": 20,
+            "xpos": 953,
+            "ypos": 71
+        }
+    ],
+    "properties": [],
+    "tags": [
+        "firefox_addon_success"
+    ]
 }