diff --git a/application/basilisk/extensions/pdfjs/content/PdfStreamConverter.jsm b/application/basilisk/extensions/pdfjs/content/PdfStreamConverter.jsm
index 55d5ccc36d..3a43ddd494 100644
--- a/application/basilisk/extensions/pdfjs/content/PdfStreamConverter.jsm
+++ b/application/basilisk/extensions/pdfjs/content/PdfStreamConverter.jsm
@@ -871,6 +871,11 @@ PdfStreamConverter.prototype = {
       aRequest.setResponseHeader("Refresh", "", false);
     }
 
+    // The document will be loaded via the stream converter as html, but we
+    // may have come here via a download/attachment path. Force inline so we
+    // don't get redirected back to the external helper service.
+    aRequest.contentDisposition = Ci.nsIChannel.DISPOSITION_FORCE_INLINE;
+
     // Creating storage for PDF data
     var contentLength = aRequest.contentLength;
     this.dataListener = new PdfDataListener(contentLength);
diff --git a/netwerk/base/nsIChannel.idl b/netwerk/base/nsIChannel.idl
index 743e942920..4ffd1aaf99 100644
--- a/netwerk/base/nsIChannel.idl
+++ b/netwerk/base/nsIChannel.idl
@@ -293,10 +293,14 @@ interface nsIChannel : nsIRequest
      * if available and if applicable. This allows determining inline versus
      * attachment.
      *
-     * Setting contentDisposition provides a hint to the channel about the
-     * disposition.  If a normal Content-Disposition header is present its
-     * value will always be used.  If it is missing the hinted value will
-     * be used if set.
+    * Setting contentDisposition provides a hint to the channel about the
+    * disposition. If the hint is DISPOSITION_ATTACHMENT and a normal
+    * Content-Disposition header is present, the hinted value will always be
+    * used. If the hint is DISPOSITION_FORCE_INLINE then the disposition is
+    * inline and the header is not used. The value from Content-Disposition
+    * header is only used when the hinted value is not DISPOSITION_INLINE or
+    * DISPOSITION_FORCE_INLINE.
+    * If the header is missing the hinted value will be used if set.
      *
      * Implementations should throw NS_ERROR_NOT_AVAILABLE if the header either
      * doesn't exist for this type of channel or is empty, and return
@@ -305,6 +309,7 @@ interface nsIChannel : nsIRequest
     attribute unsigned long contentDisposition;
     const unsigned long DISPOSITION_INLINE = 0;
     const unsigned long DISPOSITION_ATTACHMENT = 1;
+    const unsigned long DISPOSITION_FORCE_INLINE = 2;
 
     /**
      * Access to the filename portion of the Content-Disposition header if
diff --git a/netwerk/protocol/http/HttpBaseChannel.cpp b/netwerk/protocol/http/HttpBaseChannel.cpp
index 3c5fa6763a..aee8f29e9f 100644
--- a/netwerk/protocol/http/HttpBaseChannel.cpp
+++ b/netwerk/protocol/http/HttpBaseChannel.cpp
@@ -511,6 +511,14 @@ HttpBaseChannel::SetContentCharset(const nsACString& aContentCharset)
 NS_IMETHODIMP
 HttpBaseChannel::GetContentDisposition(uint32_t *aContentDisposition)
 {
+  // DISPOSITION_FORCE_INLINE is used to explicitly set inline, used by
+  // the pdf reader when loading an attachment pdf without downloading it.
+  if (mContentDispositionHint == nsIChannel::DISPOSITION_ATTACHMENT ||
+      mContentDispositionHint == nsIChannel::DISPOSITION_FORCE_INLINE) {
+    *aContentDisposition = mContentDispositionHint;
+    return NS_OK;
+  }
+
   nsresult rv;
   nsCString header;
 
diff --git a/uriloader/base/nsURILoader.cpp b/uriloader/base/nsURILoader.cpp
index 224f2219ed..d3f70ce191 100644
--- a/uriloader/base/nsURILoader.cpp
+++ b/uriloader/base/nsURILoader.cpp
@@ -41,6 +41,10 @@
 #include "nsCExternalHandlerService.h" // contains contractids for the helper app service
 
 #include "nsIMIMEHeaderParam.h"
+#include "nsIMIMEInfo.h"
+#include "nsIMIMEService.h"
+#include "nsILoadInfo.h"
+#include "nsIContentPolicy.h"
 #include "nsNetCID.h"
 
 #include "nsMimeTypes.h"
@@ -389,6 +393,36 @@ nsresult nsDocumentOpenInfo::DispatchContent(nsIRequest *request, nsISupports *
     forceExternalHandling = true;
   }
 
+  // For a PDF, check if it will be handled internally. If so, don't force
+  // external handling for top-level document loads.
+  if (forceExternalHandling &&
+      mContentType.LowerCaseEqualsASCII(APPLICATION_PDF)) {
+    nsCOMPtr<nsILoadInfo> loadInfo;
+    aChannel->GetLoadInfo(getter_AddRefs(loadInfo));
+    if (loadInfo &&
+        loadInfo->GetExternalContentPolicyType() ==
+          nsIContentPolicy::TYPE_DOCUMENT) {
+      nsCOMPtr<nsIMIMEInfo> mimeInfo;
+      nsCOMPtr<nsIMIMEService> mimeSvc(
+        do_GetService(NS_MIMESERVICE_CONTRACTID));
+      if (mimeSvc) {
+        mimeSvc->GetFromTypeAndExtension(nsLiteralCString(APPLICATION_PDF),
+                                         EmptyCString(),
+                                         getter_AddRefs(mimeInfo));
+      }
+
+      if (mimeInfo) {
+        int32_t action = nsIHandlerInfo::saveToDisk;
+        mimeInfo->GetPreferredAction(&action);
+
+        bool alwaysAsk = true;
+        mimeInfo->GetAlwaysAskBeforeHandling(&alwaysAsk);
+        forceExternalHandling =
+          alwaysAsk || action != nsIHandlerInfo::handleInternally;
+      }
+    }
+  }
+
   LOG(("  forceExternalHandling: %s", forceExternalHandling ? "yes" : "no"));
 
   // The type or data the contentListener wants.
diff --git a/uriloader/exthandler/ContentHandlerService.cpp b/uriloader/exthandler/ContentHandlerService.cpp
index 75575a7304..ec2da390b4 100644
--- a/uriloader/exthandler/ContentHandlerService.cpp
+++ b/uriloader/exthandler/ContentHandlerService.cpp
@@ -104,7 +104,9 @@ NS_IMETHODIMP RemoteHandlerApp::LaunchWithURI(nsIURI *aURI, nsIInterfaceRequesto
 
 NS_IMPL_ISUPPORTS(RemoteHandlerApp, nsIHandlerApp)
 
-static inline void CopyHanderInfoTonsIHandlerInfo(HandlerInfo info, nsIHandlerInfo* aHandlerInfo)
+static inline void
+CopyHandlerInfoTonsIHandlerInfo(const HandlerInfo& info,
+                                nsIHandlerInfo* aHandlerInfo)
 {
   HandlerApp preferredApplicationHandler = info.preferredApplicationHandler();
   nsCOMPtr<nsIHandlerApp> preferredApp(new RemoteHandlerApp(preferredApplicationHandler));
@@ -112,6 +114,8 @@ static inline void CopyHanderInfoTonsIHandlerInfo(HandlerInfo info, nsIHandlerIn
   nsCOMPtr<nsIMutableArray> possibleHandlers;
   aHandlerInfo->GetPossibleApplicationHandlers(getter_AddRefs(possibleHandlers));
   possibleHandlers->AppendElement(preferredApp, false);
+  aHandlerInfo->SetPreferredAction(info.preferredAction());
+  aHandlerInfo->SetAlwaysAskBeforeHandling(info.alwaysAskBeforeHandling());
 }
 ContentHandlerService::~ContentHandlerService()
 {
@@ -127,7 +131,7 @@ NS_IMETHODIMP ContentHandlerService::FillHandlerInfo(nsIHandlerInfo *aHandlerInf
   HandlerInfo info;
   nsIHandlerInfoToHandlerInfo(aHandlerInfo, &info);
   mHandlerServiceChild->SendFillHandlerInfo(info, nsCString(aOverrideType), &info);
-  CopyHanderInfoTonsIHandlerInfo(info, aHandlerInfo);
+  CopyHandlerInfoTonsIHandlerInfo(info, aHandlerInfo);
   return NS_OK;
 }
 
diff --git a/uriloader/exthandler/PHandlerService.ipdl b/uriloader/exthandler/PHandlerService.ipdl
index bcaab60ac3..9171ef2982 100644
--- a/uriloader/exthandler/PHandlerService.ipdl
+++ b/uriloader/exthandler/PHandlerService.ipdl
@@ -19,7 +19,7 @@ struct HandlerInfo {
   bool alwaysAskBeforeHandling;
   HandlerApp preferredApplicationHandler;
   HandlerApp[] possibleApplicationHandlers;
-  long preferredAction;
+  int32_t preferredAction;
 };
 
 sync protocol PHandlerService