diff --git a/netwerk/base/src/nsURLHelperMac.cpp b/netwerk/base/src/nsURLHelperMac.cpp
index c14c1b5cc68e..c716060b779b 100644
--- a/netwerk/base/src/nsURLHelperMac.cpp
+++ b/netwerk/base/src/nsURLHelperMac.cpp
@@ -89,6 +89,10 @@ net_GetURLSpecFromFile(nsIFile *aFile, nsACString &aURL)
     // need encoding; use %2F which is a forward slash
     escPath.ReplaceSubstring(":", "%2F");
 
+    // esc_Directory does not escape the semicolons, so if a filename 
+    // contains semicolons we need to manually escape them.
+    escPath.ReplaceSubstring(";", "%3b");
+
     escPath.Insert(prefix, 0);
 
     // XXX this should be unnecessary
diff --git a/netwerk/base/src/nsURLHelperOS2.cpp b/netwerk/base/src/nsURLHelperOS2.cpp
index 38a65d66a66f..b320a7a727cc 100644
--- a/netwerk/base/src/nsURLHelperOS2.cpp
+++ b/netwerk/base/src/nsURLHelperOS2.cpp
@@ -78,6 +78,10 @@ net_GetURLSpecFromFile(nsIFile *aFile, nsACString &result)
     else
         escPath.Assign(prefix + ePath);
 
+    // esc_Directory does not escape the semicolons, so if a filename 
+    // contains semicolons we need to manually escape them.
+    escPath.ReplaceSubstring(";", "%3b");
+
     // XXX this should be unnecessary
     if (escPath[escPath.Length() - 1] != '/') {
         PRBool dir;
diff --git a/netwerk/base/src/nsURLHelperUnix.cpp b/netwerk/base/src/nsURLHelperUnix.cpp
index 9beb1bbe7132..fd93eac5bddf 100644
--- a/netwerk/base/src/nsURLHelperUnix.cpp
+++ b/netwerk/base/src/nsURLHelperUnix.cpp
@@ -61,6 +61,10 @@ net_GetURLSpecFromFile(nsIFile *aFile, nsACString &result)
     else
         escPath.Assign(prefix + ePath);
 
+    // esc_Directory does not escape the semicolons, so if a filename 
+    // contains semicolons we need to manually escape them.
+    escPath.ReplaceSubstring(";", "%3b");
+
     // XXX this should be unnecessary
     if (escPath[escPath.Length() - 1] != '/') {
         PRBool dir;
diff --git a/netwerk/base/src/nsURLHelperWin.cpp b/netwerk/base/src/nsURLHelperWin.cpp
index 3adc5ed11516..a920bc145006 100644
--- a/netwerk/base/src/nsURLHelperWin.cpp
+++ b/netwerk/base/src/nsURLHelperWin.cpp
@@ -74,6 +74,10 @@ net_GetURLSpecFromFile(nsIFile *aFile, nsACString &result)
     else
         escPath.Assign(prefix + ePath);
 
+    // esc_Directory does not escape the semicolons, so if a filename 
+    // contains semicolons we need to manually escape them.
+    escPath.ReplaceSubstring(";", "%3b");
+
     // XXX this should be unnecessary
     if (escPath[escPath.Length() - 1] != '/') {
         PRBool dir;