--- a/dom/tv/test/mochitest/head.js
+++ b/dom/tv/test/mochitest/head.js
@@ -11,16 +11,20 @@ function setupPrefsAndPermissions(callba
 function setupPrefs(callback) {
   let xhr = new XMLHttpRequest;
   let data;
 
   xhr.open("GET", "./mock_data.json", false);
   xhr.send(null);
   if (xhr.status == 200) {
     data = xhr.responseText;
+    // Convert the JSON to text and back to eliminate whitespace.
+    data = JSON.stringify(JSON.parse(data));
+    // Preferences can only be 4000 characters in a content process.
+    ok(data.length <= 4000, "Data for preferences must be 4000 characters or less.");
   }
 
   SpecialPowers.pushPrefEnv({"set": [
                               ["dom.tv.enabled", true],
                               ["dom.ignore_webidl_scope_checks", true],
                               ["dom.testing.tv_mock_data", data]
                             ]}, function() {
     callback();

--- a/dom/tv/test/mochitest/mock_data.json
+++ b/dom/tv/test/mochitest/mock_data.json
@@ -13,87 +13,87 @@
              "serviceId": "40960",
              "type": "tv",
              "name": "TV #1",
              "number" : 1,
              "isEmergency": false,
              "isFree" : true,
              "videoFilePath": "tv1.ogv",
              "programs": [
-               {"eventId":"734475972", "title":"News of Morning",  "startTime":"1430686800", "duration":"10800", "description":"Morning News", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
-               {"eventId":"422158917", "title":"News of Midnight",  "startTime":"1431266400", "duration":"3600",  "description":"Summary of today news",  "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
-               {"eventId":"533612446", "title":"Entertainment Program",  "startTime":"1431270000", "duration":"7200",  "description":"Midnight entertainment program", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]}
+               {"eventId":"734475972", "title":"News 1",  "startTime":"1430686800", "duration":"10800", "description":"Morning News", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
+               {"eventId":"422158917", "title":"News 2",  "startTime":"1431266400", "duration":"3600",  "description":"Summary of today news",  "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
+               {"eventId":"533612446", "title":"Entertainment",  "startTime":"1431270000", "duration":"7200",  "description":"Some show", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]}
                ]
              },
              {
              "_comment": "Channel Data",
              "networkId": "32122",
              "transportStreamId": "32122",
              "serviceId": "40990",
              "type": "tv",
              "name": "TV #2",
              "number" : 2,
              "isEmergency": false,
              "isFree" : true,
              "videoFilePath": "tv2.ogv",
              "programs": [
-                 {"eventId":"931109607","title":"News of Morning",	"startTime":"1430686800",	"duration":"10800",	"description":"Provide news in morning",	"rating":"0",	"audioLanguages":["eng"],	"subtitleLanguages":["eng"]},
+                 {"eventId":"931109607","title":"News 1",	"startTime":"1430686800",	"duration":"10800",	"description":"Provide news in morning",	"rating":"0",	"audioLanguages":["eng"],	"subtitleLanguages":["eng"]},
                  {"eventId":"297834220","title":"Weekly News",	"startTime":"1431259200",	"duration":"10800",	"description":"Poopular Music program",	"rating":"0",	"audioLanguages":["eng"],	"subtitleLanguages":["eng"]},
                  {"eventId":"866886159","title":"Weekly news",	"startTime":"1431270000",	"duration":"7200",	"description":"Information program on Monday",	"rating":"0",	"audioLanguages":["eng"],	"subtitleLanguages":["eng"]}
                ]
              },
              {
              "_comment": "Channel Data",
              "networkId": "32132",
              "transportStreamId": "32132",
              "serviceId": "41020",
              "type": "tv",
              "name": "TV #3",
              "number" : 3,
              "isEmergency": false,
              "isFree" : true,
              "videoFilePath": "tv1.ogv",
              "programs": [
-               {"eventId":"734475972", "title":"News of Morning",  "startTime":"1430686800", "duration":"10800", "description":"Morning News", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
-               {"eventId":"586216742", "title":"Information Program", "startTime":"1430697600", "duration":"7200",  "description":"Provide program Information.",  "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
-               {"eventId":"533612446", "title":"Entertainment Program",  "startTime":"1431270000", "duration":"7200",  "description":"Midnight entertainment program", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]}
+               {"eventId":"734475972", "title":"News 1",  "startTime":"1430686800", "duration":"10800", "description":"Morning News", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
+               {"eventId":"586216742", "title":"Info Program", "startTime":"1430697600", "duration":"7200",  "description":"Provide program Information.",  "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
+               {"eventId":"533612446", "title":"Entertainment",  "startTime":"1431270000", "duration":"7200",  "description":"Some show", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]}
                ]
              },
              {
              "_comment": "Channel Data",
              "networkId": "32142",
              "transportStreamId": "32142",
              "serviceId": "41040",
              "type": "tv",
              "name": "TV #5",
              "number" : 4,
              "isEmergency": false,
              "isFree" : true,
              "videoFilePath": "tv2.ogv",
              "programs": [
-                 {"eventId":"931109607","title":"News of Morning",	"startTime":"1430686800",	"duration":"10800",	"description":"Provide news in morning",	"rating":"0",	"audioLanguages":["eng"],	"subtitleLanguages":["eng"]},
+                 {"eventId":"931109607","title":"News 1",	"startTime":"1430686800",	"duration":"10800",	"description":"Provide news in morning",	"rating":"0",	"audioLanguages":["eng"],	"subtitleLanguages":["eng"]},
                  {"eventId":"297834220","title":"Weekly News",	"startTime":"1431259200",	"duration":"10800",	"description":"Poopular Music program",	"rating":"0",	"audioLanguages":["eng"],	"subtitleLanguages":["eng"]},
                  {"eventId":"866886159","title":"Weekly news",	"startTime":"1431270000",	"duration":"7200",	"description":"Information program on Monday",	"rating":"0",	"audioLanguages":["eng"],	"subtitleLanguages":["eng"]}
                ]
              },
              {
              "_comment": "Channel Data",
              "networkId": "32152",
              "transportStreamId": "32152",
              "serviceId": "41060",
              "type": "tv",
              "name": "TV #5",
              "number" : 5,
              "isEmergency": false,
              "isFree" : true,
              "videoFilePath": "tv1.ogv",
              "programs": [
-               {"eventId":"734475972", "title":"News of Morning",  "startTime":"1430686800", "duration":"10800", "description":"Morning News", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
-               {"eventId":"586216742", "title":"Information Program", "startTime":"1430697600", "duration":"7200",  "description":"Provide program Information.",  "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
-               {"eventId":"533612446", "title":"Entertainment Program",  "startTime":"1431270000", "duration":"7200",  "description":"Midnight entertainment program", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]}
+               {"eventId":"734475972", "title":"News 1",  "startTime":"1430686800", "duration":"10800", "description":"Morning News", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
+               {"eventId":"586216742", "title":"Info Program", "startTime":"1430697600", "duration":"7200",  "description":"Provide program Information.",  "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]},
+               {"eventId":"533612446", "title":"Entertainment",  "startTime":"1431270000", "duration":"7200",  "description":"Some show", "rating":"0", "audioLanguages":["eng"], "subtitleLanguages":["eng"]}
                ]
              }
            ]
          }
        ]
     }
   ]
-}
\ No newline at end of file
+}