diff --git a/netwerk/base/nsStandardURL.cpp b/netwerk/base/nsStandardURL.cpp
index 4ae6fc51629..aa2cffa20ab 100644
--- a/netwerk/base/nsStandardURL.cpp
+++ b/netwerk/base/nsStandardURL.cpp
@@ -1187,6 +1187,29 @@ nsStandardURL::GetOriginCharset(nsACString &result)
     return NS_OK;
 }
 
+static bool
+IsSpecialProtocol(const nsACString &input)
+{
+    nsACString::const_iterator start, end;
+    input.BeginReading(start);
+    nsACString::const_iterator iterator(start);
+    input.EndReading(end);
+
+    while (iterator != end && *iterator != ':') {
+        iterator++;
+    }
+
+    nsAutoCString protocol(nsDependentCSubstring(start.get(), iterator.get()));
+
+    return protocol.LowerCaseEqualsLiteral("http") ||
+           protocol.LowerCaseEqualsLiteral("https") ||
+           protocol.LowerCaseEqualsLiteral("ftp") ||
+           protocol.LowerCaseEqualsLiteral("ws") ||
+           protocol.LowerCaseEqualsLiteral("wss") ||
+           protocol.LowerCaseEqualsLiteral("file") ||
+           protocol.LowerCaseEqualsLiteral("gopher");
+}
+
 NS_IMETHODIMP
 nsStandardURL::SetSpec(const nsACString &input)
 {
@@ -1217,12 +1240,35 @@ nsStandardURL::SetSpec(const nsACString &input)
     Clear();
 
     // filter out unexpected chars "\r\n\t" if necessary
-    nsAutoCString buf1;
-    if (net_FilterURIString(spec, buf1)) {
-        spec = buf1.get();
-        specLength = buf1.Length();
+    nsAutoCString filteredURI;
+    if (!net_FilterURIString(spec, filteredURI)) {
+        // Copy the content into filteredURI even if no whitespace was stripped.
+        // We need a non-const buffer to perform backslash replacement.
+        filteredURI = input;
     }
 
+    if (IsSpecialProtocol(filteredURI)) {
+        // Bug 652186: Replace all backslashes with slashes when parsing paths
+        // Stop when we reach the query or the hash.
+        nsAutoCString::iterator start;
+        nsAutoCString::iterator end;
+        filteredURI.BeginWriting(start);
+        filteredURI.EndWriting(end);
+        while (start != end) {
+            if (*start == '?' || *start == '#') {
+                break;
+            }
+            if (*start == '\\') {
+                *start = '/';
+            }
+            start++;
+        }
+    }
+
+    spec = filteredURI.get();
+    specLength = filteredURI.Length();
+
+
     // parse the given URL...
     nsresult rv = ParseURL(spec, specLength);
     if (NS_SUCCEEDED(rv)) {
@@ -2004,12 +2050,15 @@ nsStandardURL::Resolve(const nsACString &in, nsACString &out)
     // filter out unexpected chars "\r\n\t" if necessary
     nsAutoCString buf;
     int32_t relpathLen;
-    if (net_FilterURIString(relpath, buf)) {
-        relpath = buf.get();
-        relpathLen = buf.Length();
-    } else
-        relpathLen = flat.Length();
-    
+    if (!net_FilterURIString(relpath, buf)) {
+        // Copy the content into filteredURI even if no whitespace was stripped.
+        // We need a non-const buffer to perform backslash replacement.
+        buf = in;
+    }
+
+    relpath = buf.get();
+    relpathLen = buf.Length();
+
     char *result = nullptr;
 
     LOG(("nsStandardURL::Resolve [this=%p spec=%s relpath=%s]\n",
@@ -2046,6 +2095,30 @@ nsStandardURL::Resolve(const nsACString &in, nsACString &out)
     // reset the scheme and assume a relative url
     if (NS_FAILED(rv)) scheme.Reset(); 
 
+    nsAutoCString protocol(Segment(scheme));
+    nsAutoCString baseProtocol(Scheme());
+
+    // We need to do backslash replacement for the following cases:
+    // 1. The input is an absolute path with a http/https/ftp scheme
+    // 2. The input is a relative path, and the base URL has a http/https/ftp scheme
+    if ((protocol.IsEmpty() && IsSpecialProtocol(baseProtocol)) ||
+         IsSpecialProtocol(protocol)) {
+
+        nsAutoCString::iterator start;
+        nsAutoCString::iterator end;
+        buf.BeginWriting(start);
+        buf.EndWriting(end);
+        while (start != end) {
+            if (*start == '?' || *start == '#') {
+                break;
+            }
+            if (*start == '\\') {
+                *start = '/';
+            }
+            start++;
+        }
+    }
+
     if (scheme.mLen >= 0) {
         // add some flags to coalesceFlag if it is an ftp-url
         // need this later on when coalescing the resulting URL
diff --git a/netwerk/test/unit/test_standardurl.js b/netwerk/test/unit/test_standardurl.js
index ee1ee0251fe..1eaaa601438 100644
--- a/netwerk/test/unit/test_standardurl.js
+++ b/netwerk/test/unit/test_standardurl.js
@@ -333,3 +333,16 @@ add_test(function test_filterWhitespace()
   do_check_eq(url.spec, "http://example.com/path/to%20the/file.ext?query#hash");
   run_next_test();
 });
+
+add_test(function test_backslashReplacement()
+{
+  var url = stringToURL("http:\\\\test.com\\path/to\\file?query\\backslash#hash\\");
+  do_check_eq(url.spec, "http://test.com/path/to/file?query\\backslash#hash\\");
+
+  url = stringToURL("http:\\\\test.com\\example.org/path\\to/file");
+  do_check_eq(url.spec, "http://test.com/example.org/path/to/file");
+  do_check_eq(url.host, "test.com");
+  do_check_eq(url.path, "/example.org/path/to/file");
+
+  run_next_test();
+});