--- a/browser/components/nsBrowserGlue.js
+++ b/browser/components/nsBrowserGlue.js
@@ -1099,91 +1099,16 @@ BrowserGlue.prototype = {
         }
       });
     }
 
     if (AddonManager.nonMpcDisabled) {
       this._notifyDisabledNonMpc();
     }
 
-    // Perform default browser checking.
-    if (ShellService) {
-      let shouldCheck = AppConstants.DEBUG ? false :
-                                             ShellService.shouldCheckDefaultBrowser;
-
-      const skipDefaultBrowserCheck =
-        Services.prefs.getBoolPref("browser.shell.skipDefaultBrowserCheckOnFirstRun") &&
-        !Services.prefs.getBoolPref("browser.shell.didSkipDefaultBrowserCheckOnFirstRun");
-
-      const usePromptLimit = !AppConstants.RELEASE_OR_BETA;
-      let promptCount =
-        usePromptLimit ? Services.prefs.getIntPref("browser.shell.defaultBrowserCheckCount") : 0;
-
-      let willRecoverSession = false;
-      try {
-        let ss = Cc["@mozilla.org/browser/sessionstartup;1"].
-                 getService(Ci.nsISessionStartup);
-        willRecoverSession =
-          (ss.sessionType == Ci.nsISessionStartup.RECOVER_SESSION);
-      } catch (ex) { /* never mind; suppose SessionStore is broken */ }
-
-      // startup check, check all assoc
-      let isDefault = false;
-      let isDefaultError = false;
-      try {
-        isDefault = ShellService.isDefaultBrowser(true, false);
-      } catch (ex) {
-        isDefaultError = true;
-      }
-
-      if (isDefault) {
-        let now = (Math.floor(Date.now() / 1000)).toString();
-        Services.prefs.setCharPref("browser.shell.mostRecentDateSetAsDefault", now);
-      }
-
-      let willPrompt = shouldCheck && !isDefault && !willRecoverSession;
-
-      // Skip the "Set Default Browser" check during first-run or after the
-      // browser has been run a few times.
-      if (willPrompt) {
-        if (skipDefaultBrowserCheck) {
-          Services.prefs.setBoolPref("browser.shell.didSkipDefaultBrowserCheckOnFirstRun", true);
-          willPrompt = false;
-        } else {
-          promptCount++;
-        }
-        if (usePromptLimit && promptCount > 3) {
-          willPrompt = false;
-        }
-      }
-
-      if (usePromptLimit && willPrompt) {
-        Services.prefs.setIntPref("browser.shell.defaultBrowserCheckCount", promptCount);
-      }
-
-      try {
-        // Report default browser status on startup to telemetry
-        // so we can track whether we are the default.
-        Services.telemetry.getHistogramById("BROWSER_IS_USER_DEFAULT")
-                          .add(isDefault);
-        Services.telemetry.getHistogramById("BROWSER_IS_USER_DEFAULT_ERROR")
-                          .add(isDefaultError);
-        Services.telemetry.getHistogramById("BROWSER_SET_DEFAULT_ALWAYS_CHECK")
-                          .add(shouldCheck);
-        Services.telemetry.getHistogramById("BROWSER_SET_DEFAULT_DIALOG_PROMPT_RAWCOUNT")
-                          .add(promptCount);
-      } catch (ex) { /* Don't break the default prompt if telemetry is broken. */ }
-
-      if (willPrompt) {
-        Services.tm.dispatchToMainThread(function() {
-          DefaultBrowserCheck.prompt(RecentWindow.getMostRecentBrowserWindow());
-        });
-      }
-    }
-
     if (AppConstants.MOZ_CRASHREPORTER) {
       UnsubmittedCrashHandler.init();
       Services.tm.idleDispatchToMainThread(function() {
         UnsubmittedCrashHandler.checkForUnsubmittedCrashReports();
       });
     }
 
     this._sanitizer.onStartup();
@@ -1228,16 +1153,20 @@ BrowserGlue.prototype = {
       ContextualIdentityService.load();
     });
 
     // It's important that SafeBrowsing is initialized reasonably
     // early, so we use a maximum timeout for it.
     Services.tm.idleDispatchToMainThread(() => {
       SafeBrowsing.init();
     }, 5000);
+
+    Services.tm.idleDispatchToMainThread(() => {
+      this._checkForDefaultBrowser();
+    });
   },
 
   /**
    * Use this function as an entry point to schedule tasks that need
    * to run once per session, at any arbitrary point in time.
    * This function will be called from an idle observer. Check the value of
    * LATE_TASKS_IDLE_TIME_SEC to see the current value for this idle
    * observer.
@@ -2158,16 +2087,93 @@ BrowserGlue.prototype = {
         Services.prefs.setIntPref("browser.uidensity", 1);
       }
     }
 
     // Update the migration version.
     Services.prefs.setIntPref("browser.migration.version", UI_VERSION);
   },
 
+  _checkForDefaultBrowser() {
+    // Perform default browser checking.
+    if (!ShellService) {
+      return;
+    }
+
+    let shouldCheck = AppConstants.DEBUG ? false :
+                                           ShellService.shouldCheckDefaultBrowser;
+
+    const skipDefaultBrowserCheck =
+      Services.prefs.getBoolPref("browser.shell.skipDefaultBrowserCheckOnFirstRun") &&
+      !Services.prefs.getBoolPref("browser.shell.didSkipDefaultBrowserCheckOnFirstRun");
+
+    const usePromptLimit = !AppConstants.RELEASE_OR_BETA;
+    let promptCount =
+      usePromptLimit ? Services.prefs.getIntPref("browser.shell.defaultBrowserCheckCount") : 0;
+
+    let willRecoverSession = false;
+    try {
+      let ss = Cc["@mozilla.org/browser/sessionstartup;1"].
+               getService(Ci.nsISessionStartup);
+      willRecoverSession =
+        (ss.sessionType == Ci.nsISessionStartup.RECOVER_SESSION);
+    } catch (ex) { /* never mind; suppose SessionStore is broken */ }
+
+    // startup check, check all assoc
+    let isDefault = false;
+    let isDefaultError = false;
+    try {
+      isDefault = ShellService.isDefaultBrowser(true, false);
+    } catch (ex) {
+      isDefaultError = true;
+    }
+
+    if (isDefault) {
+      let now = (Math.floor(Date.now() / 1000)).toString();
+      Services.prefs.setCharPref("browser.shell.mostRecentDateSetAsDefault", now);
+    }
+
+    let willPrompt = shouldCheck && !isDefault && !willRecoverSession;
+
+    // Skip the "Set Default Browser" check during first-run or after the
+    // browser has been run a few times.
+    if (willPrompt) {
+      if (skipDefaultBrowserCheck) {
+        Services.prefs.setBoolPref("browser.shell.didSkipDefaultBrowserCheckOnFirstRun", true);
+        willPrompt = false;
+      } else {
+        promptCount++;
+      }
+      if (usePromptLimit && promptCount > 3) {
+        willPrompt = false;
+      }
+    }
+
+    if (usePromptLimit && willPrompt) {
+      Services.prefs.setIntPref("browser.shell.defaultBrowserCheckCount", promptCount);
+    }
+
+    try {
+      // Report default browser status on startup to telemetry
+      // so we can track whether we are the default.
+      Services.telemetry.getHistogramById("BROWSER_IS_USER_DEFAULT")
+                        .add(isDefault);
+      Services.telemetry.getHistogramById("BROWSER_IS_USER_DEFAULT_ERROR")
+                        .add(isDefaultError);
+      Services.telemetry.getHistogramById("BROWSER_SET_DEFAULT_ALWAYS_CHECK")
+                        .add(shouldCheck);
+      Services.telemetry.getHistogramById("BROWSER_SET_DEFAULT_DIALOG_PROMPT_RAWCOUNT")
+                        .add(promptCount);
+    } catch (ex) { /* Don't break the default prompt if telemetry is broken. */ }
+
+    if (willPrompt) {
+      DefaultBrowserCheck.prompt(RecentWindow.getMostRecentBrowserWindow());
+    }
+  },
+
   // ------------------------------
   // public nsIBrowserGlue members
   // ------------------------------
 
   sanitize: function BG_sanitize(aParentWindow) {
     this._sanitizer.sanitize(aParentWindow);
   },