Bug 197466 - "Back button (session history) has 50 entries regardless of setting in prefs.js" [p=zug_treno@yahoo.com r+sr=bzbarsky a1.9=damons]

docshell/shistory/src/nsSHistory.cpp

@@ -220,14 +220,23 @@ nsSHistory::Startup()
 {
   nsCOMPtr<nsIPrefService> prefs = do_GetService(NS_PREFSERVICE_CONTRACTID);
   if (prefs) {
-    // Session history size is only taken from the default prefs branch.
+    nsCOMPtr<nsIPrefBranch> sesHBranch;
-    // This means that it's only configurable on a per-application basis.
+    prefs->GetBranch(nsnull, getter_AddRefs(sesHBranch));
+    if (sesHBranch) {
+      sesHBranch->GetIntPref(PREF_SHISTORY_SIZE, &gHistoryMaxSize);
+    }
+
     // The goal of this is to unbreak users who have inadvertently set their
-    // session history size to -1.
+    // session history size to less than the default value.
+    PRInt32  defaultHistoryMaxSize = 50;
     nsCOMPtr<nsIPrefBranch> defaultBranch;
     prefs->GetDefaultBranch(nsnull, getter_AddRefs(defaultBranch));
     if (defaultBranch) {
-      defaultBranch->GetIntPref(PREF_SHISTORY_SIZE, &gHistoryMaxSize);
+      defaultBranch->GetIntPref(PREF_SHISTORY_SIZE, &defaultHistoryMaxSize);
+    }
+
+    if (gHistoryMaxSize < defaultHistoryMaxSize) {
+      gHistoryMaxSize = defaultHistoryMaxSize;
     }
     
     // Allow the user to override the max total number of cached viewers,