Backed out changeset 2c633215c514 (bug 1482055) for causing bug 1500505.

browser/modules/Sanitizer.jsm

@@ -711,14 +711,6 @@ async function sanitizeSessionPrincipals() {
     return;
   }
 
-  // When PREF_COOKIE_LIFETIME is set to ACCEPT_SESSION, any new cookie will be
-  // marked as session only. But we don't touch the existing ones. For this
-  // reason, here we delete any existing cookie, at shutdown.
-  await new Promise(resolve => {
-    Services.clearData.deleteData(Ci.nsIClearDataService.CLEAR_COOKIES,
-                                  resolve);
-  });
-
   let principals = await new Promise(resolve => {
     quotaManagerService.getUsage(request => {
       if (request.resultCode != Cr.NS_OK) {