diff --git a/mozilla/modules/libjar/nsJARChannel.cpp b/mozilla/modules/libjar/nsJARChannel.cpp
index ee2244b5e6a..550db4e440a 100644
--- a/mozilla/modules/libjar/nsJARChannel.cpp
+++ b/mozilla/modules/libjar/nsJARChannel.cpp
@@ -449,7 +449,7 @@ nsJARChannel::EnsureJARFileAvailable(OnJARFileAvailableFun onJARFileAvailable,
     if (NS_FAILED(rv)) goto error;
 
     rv = jarBaseChannel->GetLocalFile(getter_AddRefs(jarCacheFile));
-    if (NS_SUCCEEDED(rv)) {
+    if (NS_SUCCEEDED(rv) && jarCacheFile) {
         // Case 1: Local file
         // we've already got a local jar file -- no need to download it
 
diff --git a/mozilla/modules/libjar/nsJARURI.cpp b/mozilla/modules/libjar/nsJARURI.cpp
index 98e8fb74e41..34ef86d3bec 100644
--- a/mozilla/modules/libjar/nsJARURI.cpp
+++ b/mozilla/modules/libjar/nsJARURI.cpp
@@ -243,6 +243,9 @@ nsJARURI::Equals(nsIURI *other, PRBool *result)
     nsresult rv;
     *result = PR_FALSE;
 
+    if (other == nsnull)
+        return NS_OK;	// not equal
+
     nsJARURI* otherJAR;
     rv = other->QueryInterface(NS_GET_IID(nsIJARURI), (void**)&otherJAR);
     if (NS_FAILED(rv))
diff --git a/mozilla/netwerk/protocol/jar/src/nsJARChannel.cpp b/mozilla/netwerk/protocol/jar/src/nsJARChannel.cpp
index ee2244b5e6a..550db4e440a 100644
--- a/mozilla/netwerk/protocol/jar/src/nsJARChannel.cpp
+++ b/mozilla/netwerk/protocol/jar/src/nsJARChannel.cpp
@@ -449,7 +449,7 @@ nsJARChannel::EnsureJARFileAvailable(OnJARFileAvailableFun onJARFileAvailable,
     if (NS_FAILED(rv)) goto error;
 
     rv = jarBaseChannel->GetLocalFile(getter_AddRefs(jarCacheFile));
-    if (NS_SUCCEEDED(rv)) {
+    if (NS_SUCCEEDED(rv) && jarCacheFile) {
         // Case 1: Local file
         // we've already got a local jar file -- no need to download it
 
diff --git a/mozilla/netwerk/protocol/jar/src/nsJARURI.cpp b/mozilla/netwerk/protocol/jar/src/nsJARURI.cpp
index 98e8fb74e41..34ef86d3bec 100644
--- a/mozilla/netwerk/protocol/jar/src/nsJARURI.cpp
+++ b/mozilla/netwerk/protocol/jar/src/nsJARURI.cpp
@@ -243,6 +243,9 @@ nsJARURI::Equals(nsIURI *other, PRBool *result)
     nsresult rv;
     *result = PR_FALSE;
 
+    if (other == nsnull)
+        return NS_OK;	// not equal
+
     nsJARURI* otherJAR;
     rv = other->QueryInterface(NS_GET_IID(nsIJARURI), (void**)&otherJAR);
     if (NS_FAILED(rv))