diff --git a/uriloader/exthandler/nsExternalHelperAppService.cpp b/uriloader/exthandler/nsExternalHelperAppService.cpp
--- a/uriloader/exthandler/nsExternalHelperAppService.cpp
+++ b/uriloader/exthandler/nsExternalHelperAppService.cpp
@@ -2590,26 +2590,21 @@ NS_IMETHODIMP nsExternalHelperAppService
         }
       }
     }
   }
 
   // (3) No match yet. Ask extras.
   if (!found) {
     rv = NS_ERROR_FAILURE;
-#ifdef XP_WIN
-    /* XXX Gross hack to wallpaper over the most common Win32
-     * extension issues caused by the fix for bug 116938.  See bug
-     * 120327, comment 271 for why this is needed.  Not even sure we
-     * want to remove this once we have fixed all this stuff to work
-     * right; any info we get from extras on this type is pretty much
-     * useless....
-     */
+    // Getting info for application/octet-stream content-type from extras
+    // does not make a sense because this tends to open all octet-streams
+    // as Binary file with exe, com or bin extension regardless the real
+    // extension.
     if (!typeToUse.Equals(APPLICATION_OCTET_STREAM, nsCaseInsensitiveCStringComparator()))
-#endif
       rv = FillMIMEInfoForMimeTypeFromExtras(typeToUse, *_retval);
     LOG(("Searched extras (by type), rv 0x%08" PRIX32 "\n", static_cast<uint32_t>(rv)));
     // If that didn't work out, try file extension from extras
     if (NS_FAILED(rv) && !aFileExt.IsEmpty()) {
       rv = FillMIMEInfoForExtensionFromExtras(aFileExt, *_retval);
       LOG(("Searched extras (by ext), rv 0x%08" PRIX32 "\n", static_cast<uint32_t>(rv)));
     }
     // If that still didn't work, set the file description to "ext File"
diff --git a/uriloader/exthandler/unix/nsOSHelperAppService.cpp b/uriloader/exthandler/unix/nsOSHelperAppService.cpp
--- a/uriloader/exthandler/unix/nsOSHelperAppService.cpp
+++ b/uriloader/exthandler/unix/nsOSHelperAppService.cpp
@@ -26,16 +26,17 @@
 #include "nsISupportsPrimitives.h"
 #include "nsCRT.h"
 #include "nsDirectoryServiceDefs.h"
 #include "nsDirectoryServiceUtils.h"
 #include "ContentHandlerService.h"
 #include "prenv.h"      // for PR_GetEnv()
 #include "nsAutoPtr.h"
 #include "mozilla/Preferences.h"
+#include "nsMimeTypes.h"
 
 using namespace mozilla;
 
 #define LOG(args) MOZ_LOG(mLog, mozilla::LogLevel::Debug, args)
 #define LOG_ENABLED() MOZ_LOG_TEST(mLog, mozilla::LogLevel::Debug)
 
 static nsresult
 FindSemicolon(nsAString::const_iterator& aSemicolon_iter,
@@ -1445,17 +1446,22 @@ nsOSHelperAppService::GetFromType(const 
 }
 
 
 already_AddRefed<nsIMIMEInfo>
 nsOSHelperAppService::GetMIMEInfoFromOS(const nsACString& aType,
                                         const nsACString& aFileExt,
                                         bool       *aFound) {
   *aFound = true;
-  RefPtr<nsMIMEInfoBase> retval = GetFromType(PromiseFlatCString(aType));
+  RefPtr<nsMIMEInfoBase> retval;
+  // Fallback to lookup by extension when generic 'application/octet-stream'
+  // content type is received.
+  if (!aType.EqualsLiteral(APPLICATION_OCTET_STREAM)) {
+    retval = GetFromType(PromiseFlatCString(aType));
+  }
   bool hasDefault = false;
   if (retval)
     retval->GetHasDefaultHandler(&hasDefault);
   if (!retval || !hasDefault) {
     RefPtr<nsMIMEInfoBase> miByExt = GetFromExtension(PromiseFlatCString(aFileExt));
     // If we had no extension match, but a type match, use that
     if (!miByExt && retval)
       return retval.forget();