--- a/browser/actors/ContextMenuChild.jsm
+++ b/browser/actors/ContextMenuChild.jsm
@@ -218,16 +218,18 @@ class ContextMenuChild extends JSWindowA
           "canvas"
         );
         canvas.width = video.videoWidth;
         canvas.height = video.videoHeight;
 
         let ctxDraw = canvas.getContext("2d");
         ctxDraw.drawImage(video, 0, 0);
 
+        // Note: if changing the content type, don't forget to update
+        // consumers that also hardcode this content type.
         return Promise.resolve(canvas.toDataURL("image/jpeg", ""));
       }
 
       case "ContextMenu:SetAsDesktopBackground": {
         let target = ContentDOMReference.resolve(message.data.targetIdentifier);
 
         // Paranoia: check disableSetDesktopBackground again, in case the
         // image changed since the context menu was initiated.

--- a/browser/base/content/nsContextMenu.js
+++ b/browser/base/content/nsContextMenu.js
@@ -1280,17 +1280,17 @@ class nsContextMenu {
       saveImageURL(
         dataURL,
         name,
         "SaveImageTitle",
         true, // bypass cache
         false, // don't skip prompt for where to save
         referrerInfo, // referrer info
         null, // document
-        null, // content type
+        "image/jpeg", // content type - keep in sync with ContextMenuChild!
         null, // content disposition
         isPrivate,
         this.principal
       );
     });
   }
 
   leaveDOMFullScreen() {
@@ -1588,17 +1588,17 @@ class nsContextMenu {
         saveImageURL(
           blobURL,
           "canvas.png",
           "SaveImageTitle",
           true,
           false,
           referrerInfo,
           null,
-          null,
+          "image/png", // _canvasToBlobURL uses image/png by default.
           null,
           isPrivate,
           document.nodePrincipal /* system, because blob: */
         );
       }, Cu.reportError);
     } else if (this.onImage) {
       urlSecurityCheck(this.mediaURL, this.principal);
       saveImageURL(

--- a/browser/components/shell/nsMacShellService.cpp
+++ b/browser/components/shell/nsMacShellService.cpp
@@ -148,17 +148,18 @@ nsMacShellService::SetDesktopBackground(
   if (docShell) {
     loadContext = do_QueryInterface(docShell);
   }
 
   nsCOMPtr<nsIReferrerInfo> referrerInfo = new mozilla::dom::ReferrerInfo();
   referrerInfo->InitWithNode(aElement);
 
   return wbp->SaveURI(imageURI, aElement->NodePrincipal(), 0, referrerInfo,
-                      nullptr, nullptr, mBackgroundFile, loadContext);
+                      nullptr, nullptr, mBackgroundFile,
+                      nsIContentPolicy::TYPE_IMAGE, loadContext);
 }
 
 NS_IMETHODIMP
 nsMacShellService::OnProgressChange(nsIWebProgress* aWebProgress,
                                     nsIRequest* aRequest,
                                     int32_t aCurSelfProgress,
                                     int32_t aMaxSelfProgress,
                                     int32_t aCurTotalProgress,

--- a/dom/base/nsContentAreaDragDrop.cpp
+++ b/dom/base/nsContentAreaDragDrop.cpp
@@ -23,16 +23,17 @@
 #include "nsISupportsPrimitives.h"
 #include "nsServiceManagerUtils.h"
 #include "nsNetUtil.h"
 #include "nsIFile.h"
 #include "nsFrameLoader.h"
 #include "nsFrameLoaderOwner.h"
 #include "nsIContent.h"
 #include "nsIContentInlines.h"
+#include "nsIContentPolicy.h"
 #include "nsIImageLoadingContent.h"
 #include "nsUnicharUtils.h"
 #include "nsIURL.h"
 #include "nsIURIMutator.h"
 #include "mozilla/dom/Document.h"
 #include "nsIPrincipal.h"
 #include "nsIWebBrowserPersist.h"
 #include "nsEscape.h"
@@ -122,17 +123,18 @@ nsresult nsContentAreaDragDrop::GetDragD
 
 NS_IMPL_ISUPPORTS(nsContentAreaDragDropDataProvider, nsIFlavorDataProvider)
 
 // SaveURIToFile
 // used on platforms where it's possible to drag items (e.g. images)
 // into the file system
 nsresult nsContentAreaDragDropDataProvider::SaveURIToFile(
     nsIURI* inSourceURI, nsIPrincipal* inTriggeringPrincipal,
-    nsIFile* inDestFile, bool isPrivate) {
+    nsIFile* inDestFile, nsContentPolicyType inContentPolicyType,
+    bool isPrivate) {
   nsCOMPtr<nsIURL> sourceURL = do_QueryInterface(inSourceURI);
   if (!sourceURL) {
     return NS_ERROR_NO_INTERFACE;
   }
 
   nsresult rv = inDestFile->CreateUnique(nsIFile::NORMAL_FILE_TYPE, 0600);
   NS_ENSURE_SUCCESS(rv, rv);
 
@@ -143,17 +145,17 @@ nsresult nsContentAreaDragDropDataProvid
   NS_ENSURE_SUCCESS(rv, rv);
 
   persist->SetPersistFlags(
       nsIWebBrowserPersist::PERSIST_FLAGS_AUTODETECT_APPLY_CONVERSION);
 
   // referrer policy can be anything since the referrer is nullptr
   return persist->SavePrivacyAwareURI(inSourceURI, inTriggeringPrincipal, 0,
                                       nullptr, nullptr, nullptr, inDestFile,
-                                      isPrivate);
+                                      inContentPolicyType, isPrivate);
 }
 
 /*
  * Check if the provided filename extension is valid for the MIME type and
  * return the MIME type's primary extension.
  *
  * @param aExtension           [in]  the extension to check
  * @param aMimeType            [in]  the MIME type to check the extension with
@@ -308,17 +310,20 @@ nsContentAreaDragDropDataProvider::GetFl
     rv = destDirectory->Clone(getter_AddRefs(file));
     NS_ENSURE_SUCCESS(rv, rv);
 
     file->Append(targetFilename);
 
     bool isPrivate = aTransferable->GetIsPrivateData();
 
     nsCOMPtr<nsIPrincipal> principal = aTransferable->GetRequestingPrincipal();
-    rv = SaveURIToFile(sourceURI, principal, file, isPrivate);
+    nsContentPolicyType contentPolicyType =
+        aTransferable->GetContentPolicyType();
+    rv =
+        SaveURIToFile(sourceURI, principal, file, contentPolicyType, isPrivate);
     // send back an nsIFile
     if (NS_SUCCEEDED(rv)) {
       CallQueryInterface(file, aData);
     }
   }
 
   return rv;
 }

--- a/dom/base/nsContentAreaDragDrop.h
+++ b/dom/base/nsContentAreaDragDrop.h
@@ -68,12 +68,13 @@ class nsContentAreaDragDropDataProvider 
   virtual ~nsContentAreaDragDropDataProvider() {}
 
  public:
   NS_DECL_ISUPPORTS
   NS_DECL_NSIFLAVORDATAPROVIDER
 
   nsresult SaveURIToFile(nsIURI* inSourceURI,
                          nsIPrincipal* inTriggeringPrincipal,
-                         nsIFile* inDestFile, bool isPrivate);
+                         nsIFile* inDestFile, nsContentPolicyType inPolicyType,
+                         bool isPrivate);
 };
 
 #endif /* nsContentAreaDragDrop_h__ */

--- a/dom/tests/browser/browser.ini
+++ b/dom/tests/browser/browser.ini
@@ -67,16 +67,17 @@ fail-if = fission
 skip-if =
   !e10s || # This is a test of e10s functionality.
   (fission && debug) # Intermittently fails uncleanly and breaks subsequent tests.
 [browser_persist_cookies.js]
 support-files =
   set-samesite-cookies-and-redirect.sjs
   mimeme.sjs
 skip-if = fission
+[browser_persist_image_accept.js]
 [browser_persist_mixed_content_image.js]
 support-files =
   test_mixed_content_image.html
   dummy.png
 [browser_pointerlock_warning.js]
 [browser_test_focus_after_modal_state.js]
 skip-if = verify
 support-files =

new file mode 100644
--- /dev/null
+++ b/dom/tests/browser/browser_persist_image_accept.js
@@ -0,0 +1,128 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_PATH = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "https://example.org"
+);
+
+var MockFilePicker = SpecialPowers.MockFilePicker;
+MockFilePicker.init(window);
+
+registerCleanupFunction(async function() {
+  info("Running the cleanup code");
+  MockFilePicker.cleanup();
+  if (gTestDir && gTestDir.exists()) {
+    // On Windows, sometimes nsIFile.remove() throws, probably because we're
+    // still writing to the directory we're trying to remove, despite
+    // waiting for the download to complete. Just retry a bit later...
+    let succeeded = false;
+    while (!succeeded) {
+      try {
+        gTestDir.remove(true);
+        succeeded = true;
+      } catch (ex) {
+        await new Promise(requestAnimationFrame);
+      }
+    }
+  }
+});
+
+let gTestDir = null;
+
+function createTemporarySaveDirectory() {
+  var saveDir = Services.dirsvc.get("TmpD", Ci.nsIFile);
+  saveDir.append("testsavedir");
+  if (!saveDir.exists()) {
+    info("create testsavedir!");
+    saveDir.create(Ci.nsIFile.DIRECTORY_TYPE, 0o755);
+  }
+  info("return from createTempSaveDir: " + saveDir.path);
+  return saveDir;
+}
+
+add_task(async function test_image_download() {
+  await BrowserTestUtils.withNewTab(TEST_PATH + "dummy.html", async browser => {
+    // Add the image, and wait for it to load.
+    await SpecialPowers.spawn(browser, [], async function() {
+      let loc = content.document.location.href;
+      let imgloc = new content.URL("dummy.png", loc);
+      let img = content.document.createElement("img");
+      img.src = imgloc;
+      await new Promise(resolve => {
+        img.onload = resolve;
+        content.document.body.appendChild(img);
+      });
+    });
+    gTestDir = createTemporarySaveDirectory();
+
+    let destFile = gTestDir.clone();
+
+    MockFilePicker.displayDirectory = gTestDir;
+    let fileName;
+    MockFilePicker.showCallback = function(fp) {
+      info("showCallback");
+      fileName = fp.defaultString;
+      info("fileName: " + fileName);
+      destFile.append(fileName);
+      info("path: " + destFile.path);
+      MockFilePicker.setFiles([destFile]);
+      MockFilePicker.filterIndex = 0; // just save the file
+      info("done showCallback");
+    };
+    let publicDownloads = await Downloads.getList(Downloads.PUBLIC);
+    let downloadFinishedPromise = new Promise(resolve => {
+      publicDownloads.addView({
+        onDownloadChanged(download) {
+          info("Download changed!");
+          if (download.succeeded || download.error) {
+            info("Download succeeded or errored");
+            publicDownloads.removeView(this);
+            publicDownloads.removeFinished();
+            resolve(download);
+          }
+        },
+      });
+    });
+    let httpOnModifyPromise = TestUtils.topicObserved(
+      "http-on-modify-request",
+      (s, t, d) => {
+        let channel = s.QueryInterface(Ci.nsIChannel);
+        let uri = channel.URI && channel.URI.spec;
+        if (!uri.endsWith("dummy.png")) {
+          info("Ignoring request for " + uri);
+          return false;
+        }
+        ok(channel instanceof Ci.nsIHttpChannel, "Should be HTTP channel");
+        channel.QueryInterface(Ci.nsIHttpChannel);
+        is(
+          channel.getRequestHeader("Accept"),
+          Services.prefs.getCharPref("image.http.accept"),
+          "Header should be image header"
+        );
+        return true;
+      }
+    );
+    // open the context menu.
+    let popup = document.getElementById("contentAreaContextMenu");
+    let popupShown = BrowserTestUtils.waitForEvent(popup, "popupshown");
+    BrowserTestUtils.synthesizeMouseAtCenter(
+      "img",
+      { type: "contextmenu", button: 2 },
+      browser
+    );
+    await popupShown;
+    let popupHidden = BrowserTestUtils.waitForEvent(popup, "popuphidden");
+    popup.querySelector("#context-saveimage").click();
+    popup.hidePopup();
+    await popupHidden;
+    info("Context menu hidden, waiting for download to finish");
+    let imageDownload = await downloadFinishedPromise;
+    ok(imageDownload.succeeded, "Image should have downloaded successfully");
+    info("Waiting for http request to complete.");
+    // Ensure we got the http request:
+    await httpOnModifyPromise;
+  });
+});

--- a/dom/tests/browser/browser_persist_mixed_content_image.js
+++ b/dom/tests/browser/browser_persist_mixed_content_image.js
@@ -70,25 +70,25 @@ add_task(async function test_image_downl
         fileName = fp.defaultString;
         info("fileName: " + fileName);
         destFile.append(fileName);
         info("path: " + destFile.path);
         MockFilePicker.setFiles([destFile]);
         MockFilePicker.filterIndex = 0; // just save the file
         info("done showCallback");
       };
-      let downloadFinishedPromise = new Promise(async resolve => {
-        let dls = await Downloads.getList(Downloads.PUBLIC);
-        dls.addView({
+      let publicDownloads = await Downloads.getList(Downloads.PUBLIC);
+      let downloadFinishedPromise = new Promise(resolve => {
+        publicDownloads.addView({
           onDownloadChanged(download) {
             info("Download changed!");
             if (download.succeeded || download.error) {
               info("Download succeeded or errored");
-              dls.removeView(this);
-              dls.removeFinished();
+              publicDownloads.removeView(this);
+              publicDownloads.removeFinished();
               resolve(download);
             }
           },
         });
       });
       // open the context menu.
       let popup = document.getElementById("contentAreaContextMenu");
       let popupShown = BrowserTestUtils.waitForEvent(popup, "popupshown");

--- a/dom/webbrowserpersist/nsIWebBrowserPersist.idl
+++ b/dom/webbrowserpersist/nsIWebBrowserPersist.idl
@@ -1,15 +1,16 @@
 /* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
  *
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsICancelable.idl"
+#include "nsIContentPolicy.idl"
 
 interface nsIURI;
 interface nsIInputStream;
 interface nsIWebProgressListener;
 interface nsIFile;
 interface nsIChannel;
 interface nsILoadContext;
 interface nsIPrincipal;
@@ -119,16 +120,17 @@ interface nsIWebBrowserPersist : nsICanc
    *                   HTTP Referer header.
    * @param aPostData  Post data to pass with an HTTP request or
    *                   <CODE>nullptr</CODE>.
    * @param aExtraHeaders Additional headers to supply with an HTTP request
    *                   or <CODE>nullptr</CODE>.
    * @param aFile      Target file. This may be a nsIFile object or an
    *                   nsIURI object with a file scheme or a scheme that
    *                   supports uploading (e.g. ftp).
+   * @param aContentPolicyType The type of content we're saving.
    * @param aPrivacyContext A context from which the privacy status of this
    *                   save operation can be determined. Must only be null
    *                   in situations in which no such context is available
    *                   (eg. the operation has no logical association with any
    *                   window or document)
    *
    * @see nsIFile
    * @see nsIURI
@@ -136,29 +138,31 @@ interface nsIWebBrowserPersist : nsICanc
    *
    * @throws NS_ERROR_INVALID_ARG One or more arguments was invalid.
    */
   void saveURI(in nsIURI aURI, in nsIPrincipal aTriggeringPrincipal,
       in unsigned long aCacheKey,
       in nsIReferrerInfo aReferrerInfo,
       in nsIInputStream aPostData,
       in string aExtraHeaders, in nsISupports aFile,
+      in nsContentPolicyType aContentPolicyType,
       in nsILoadContext aPrivacyContext);
 
   /**
    * @param aIsPrivate Treat the save operation as private (ie. with
    *                   regards to networking operations and persistence
    *                   of intermediate data, etc.)
    * @see saveURI for all other parameter descriptions
    */
   void savePrivacyAwareURI(in nsIURI aURI,
       in nsIPrincipal aTriggeringPrincipal, in unsigned long aCacheKey,
       in nsIReferrerInfo aReferrerInfo,
       in nsIInputStream aPostData,
       in string aExtraHeaders, in nsISupports aFile,
+      in nsContentPolicyType aContentPolicyType,
       in boolean aIsPrivate);
 
   /**
    * Save a channel to a file. It must not be opened yet.
    * @see saveURI
    */
   void saveChannel(in nsIChannel aChannel, in nsISupports aFile);
 

--- a/dom/webbrowserpersist/nsWebBrowserPersist.cpp
+++ b/dom/webbrowserpersist/nsWebBrowserPersist.cpp
@@ -354,39 +354,41 @@ NS_IMETHODIMP nsWebBrowserPersist::SetPr
   mEventSink = do_GetInterface(aProgressListener);
   return NS_OK;
 }
 
 NS_IMETHODIMP nsWebBrowserPersist::SaveURI(
     nsIURI* aURI, nsIPrincipal* aPrincipal, uint32_t aCacheKey,
     nsIReferrerInfo* aReferrerInfo, nsIInputStream* aPostData,
     const char* aExtraHeaders, nsISupports* aFile,
-    nsILoadContext* aPrivacyContext) {
+    nsContentPolicyType aContentPolicyType, nsILoadContext* aPrivacyContext) {
   bool isPrivate = aPrivacyContext && aPrivacyContext->UsePrivateBrowsing();
   return SavePrivacyAwareURI(aURI, aPrincipal, aCacheKey, aReferrerInfo,
-                             aPostData, aExtraHeaders, aFile, isPrivate);
+                             aPostData, aExtraHeaders, aFile,
+                             aContentPolicyType, isPrivate);
 }
 
 NS_IMETHODIMP nsWebBrowserPersist::SavePrivacyAwareURI(
     nsIURI* aURI, nsIPrincipal* aPrincipal, uint32_t aCacheKey,
     nsIReferrerInfo* aReferrerInfo, nsIInputStream* aPostData,
-    const char* aExtraHeaders, nsISupports* aFile, bool aIsPrivate) {
+    const char* aExtraHeaders, nsISupports* aFile,
+    nsContentPolicyType aContentPolicy, bool aIsPrivate) {
   NS_ENSURE_TRUE(mFirstAndOnlyUse, NS_ERROR_FAILURE);
   mFirstAndOnlyUse = false;  // Stop people from reusing this object!
 
   nsCOMPtr<nsIURI> fileAsURI;
   nsresult rv;
   rv = GetValidURIFromObject(aFile, getter_AddRefs(fileAsURI));
   NS_ENSURE_SUCCESS(rv, NS_ERROR_INVALID_ARG);
 
   // SaveURI doesn't like broken uris.
   mPersistFlags |= PERSIST_FLAGS_FAIL_ON_BROKEN_LINKS;
-  rv = SaveURIInternal(aURI, aPrincipal, nsIContentPolicy::TYPE_SAVEAS_DOWNLOAD,
-                       aCacheKey, aReferrerInfo, aPostData, aExtraHeaders,
-                       fileAsURI, false, aIsPrivate);
+  rv = SaveURIInternal(aURI, aPrincipal, aContentPolicy, aCacheKey,
+                       aReferrerInfo, aPostData, aExtraHeaders, fileAsURI,
+                       false, aIsPrivate);
   return NS_FAILED(rv) ? rv : NS_OK;
 }
 
 NS_IMETHODIMP nsWebBrowserPersist::SaveChannel(nsIChannel* aChannel,
                                                nsISupports* aFile) {
   NS_ENSURE_TRUE(mFirstAndOnlyUse, NS_ERROR_FAILURE);
   mFirstAndOnlyUse = false;  // Stop people from reusing this object!
 

--- a/toolkit/components/browser/nsWebBrowser.cpp
+++ b/toolkit/components/browser/nsWebBrowser.cpp
@@ -728,28 +728,32 @@ nsWebBrowser::SetProgressListener(nsIWeb
   mProgressListener = aProgressListener;
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsWebBrowser::SaveURI(nsIURI* aURI, nsIPrincipal* aPrincipal,
                       uint32_t aCacheKey, nsIReferrerInfo* aReferrerInfo,
                       nsIInputStream* aPostData, const char* aExtraHeaders,
-                      nsISupports* aFile, nsILoadContext* aPrivacyContext) {
+                      nsISupports* aFile,
+                      nsContentPolicyType aContentPolicyType,
+                      nsILoadContext* aPrivacyContext) {
   return SavePrivacyAwareURI(
       aURI, aPrincipal, aCacheKey, aReferrerInfo, aPostData, aExtraHeaders,
-      aFile, aPrivacyContext && aPrivacyContext->UsePrivateBrowsing());
+      aFile, aContentPolicyType,
+      aPrivacyContext && aPrivacyContext->UsePrivateBrowsing());
 }
 
 NS_IMETHODIMP
 nsWebBrowser::SavePrivacyAwareURI(nsIURI* aURI, nsIPrincipal* aPrincipal,
                                   uint32_t aCacheKey,
                                   nsIReferrerInfo* aReferrerInfo,
                                   nsIInputStream* aPostData,
                                   const char* aExtraHeaders, nsISupports* aFile,
+                                  nsContentPolicyType aContentPolicyType,
                                   bool aIsPrivate) {
   if (mPersist) {
     uint32_t currentState;
     mPersist->GetCurrentState(&currentState);
     if (currentState == PERSIST_STATE_FINISHED) {
       mPersist = nullptr;
     } else {
       // You can't save again until the last save has completed
@@ -772,17 +776,17 @@ nsWebBrowser::SavePrivacyAwareURI(nsIURI
   mPersist = do_CreateInstance(NS_WEBBROWSERPERSIST_CONTRACTID, &rv);
   NS_ENSURE_SUCCESS(rv, rv);
   mPersist->SetProgressListener(this);
   mPersist->SetPersistFlags(mPersistFlags);
   mPersist->GetCurrentState(&mPersistCurrentState);
 
   rv = mPersist->SavePrivacyAwareURI(uri, aPrincipal, aCacheKey, aReferrerInfo,
                                      aPostData, aExtraHeaders, aFile,
-                                     aIsPrivate);
+                                     aContentPolicyType, aIsPrivate);
   if (NS_FAILED(rv)) {
     mPersist = nullptr;
   }
   return rv;
 }
 
 NS_IMETHODIMP
 nsWebBrowser::SaveChannel(nsIChannel* aChannel, nsISupports* aFile) {

--- a/toolkit/components/downloads/test/unit/head.js
+++ b/toolkit/components/downloads/test/unit/head.js
@@ -415,16 +415,17 @@ function promiseStartLegacyDownload(aSou
         persist.savePrivacyAwareURI(
           sourceURI,
           Services.scriptSecurityManager.getSystemPrincipal(),
           0,
           referrerInfo,
           null,
           null,
           targetFile,
+          Ci.nsIContentPolicy.TYPE_SAVEAS_DOWNLOAD,
           isPrivate
         );
       })
       .catch(do_report_unexpected_exception);
   });
 }
 
 /**

--- a/toolkit/components/viewsource/content/viewSourceUtils.js
+++ b/toolkit/components/viewsource/content/viewSourceUtils.js
@@ -249,16 +249,17 @@ var gViewSourceUtils = {
           webBrowserPersist.savePrivacyAwareURI(
             uri,
             principal,
             null,
             null,
             null,
             null,
             file,
+            Ci.nsIContentPolicy.TYPE_SAVEAS_DOWNLOAD,
             data.isPrivate
           );
 
           let helperService = Cc[
             "@mozilla.org/uriloader/external-helper-app-service;1"
           ].getService(Ci.nsPIExternalAppLauncher);
           if (data.isPrivate) {
             // register the file to be deleted when possible

--- a/toolkit/content/contentAreaUtils.js
+++ b/toolkit/content/contentAreaUtils.js
@@ -461,16 +461,17 @@ function internalSave(
   if (aCacheKey == undefined) {
     aCacheKey = 0;
   }
 
   // Note: aDocument == null when this code is used by save-link-as...
   var saveMode = GetSaveModeForContentType(aContentType, aDocument);
 
   var file, sourceURI, saveAsType;
+  let contentPolicyType = Ci.nsIContentPolicy.TYPE_SAVEAS_DOWNLOAD;
   // Find the URI object for aURL and the FileName/Extension to use when saving.
   // FileName/Extension will be ignored if aChosenData supplied.
   if (aChosenData) {
     file = aChosenData.file;
     sourceURI = aChosenData.uri;
     saveAsType = kSaveAsType_Complete;
 
     continueSave();
@@ -485,16 +486,19 @@ function internalSave(
       aURL,
       charset,
       aDocument,
       aContentType,
       aContentDisposition
     );
     sourceURI = fileInfo.uri;
 
+    if (aContentType && aContentType.startsWith("image/")) {
+      contentPolicyType = Ci.nsIContentPolicy.TYPE_IMAGE;
+    }
     var fpParams = {
       fpTitleKey: aFilePickerTitleKey,
       fileInfo,
       contentType: aContentType,
       saveMode,
       saveAsType: kSaveAsType_Complete,
       file,
     };
@@ -553,16 +557,17 @@ function internalSave(
       sourcePrincipal,
       sourceReferrerInfo: aReferrerInfo,
       sourceDocument: useSaveDocument ? aDocument : null,
       targetContentType: saveAsType == kSaveAsType_Text ? "text/plain" : null,
       targetFile: file,
       sourceCacheKey: aCacheKey,
       sourcePostData: nonCPOWDocument ? getPostData(aDocument) : null,
       bypassCache: aShouldBypassCache,
+      contentPolicyType,
       isPrivate,
     };
 
     // Start the actual save process
     internalPersist(persistArgs);
   }
 }
 
@@ -581,16 +586,19 @@ function internalSave(
  *        the nsIReferrerInfo of the referrer info to use, or null if no
  *        referrer should be sent.
  * @param persistArgs.sourcePostData
  *        Required and used only when persistArgs.sourceDocument is NOT present,
  *        represents the POST data to be sent along with the HTTP request, and
  *        must be null if no POST data should be sent.
  * @param persistArgs.targetFile
  *        The nsIFile of the file to create
+ * @param persistArgs.contentPolicyType
+ *        The type of content we're saving. Will be used to determine what
+ *        content is accepted, enforce sniffing restrictions, etc.
  * @param persistArgs.targetContentType
  *        Required and used only when persistArgs.sourceDocument is present,
  *        determines the final content type of the saved file, or null to use
  *        the same content type as the source document. Currently only
  *        "text/plain" is meaningful.
  * @param persistArgs.bypassCache
  *        If true, the document will always be refetched from the server
  * @param persistArgs.isPrivate
@@ -666,16 +674,17 @@ function internalPersist(persistArgs) {
     persist.savePrivacyAwareURI(
       persistArgs.sourceURI,
       persistArgs.sourcePrincipal,
       persistArgs.sourceCacheKey,
       persistArgs.sourceReferrerInfo,
       persistArgs.sourcePostData,
       null,
       targetFileURL,
+      persistArgs.contentPolicyType || Ci.nsIContentPolicy.TYPE_SAVEAS_DOWNLOAD,
       persistArgs.isPrivate
     );
   }
 }
 
 /**
  * Structure for holding info about automatically supplied parameters for
  * internalSave(...). This allows parameters to be supplied so the user does not

--- a/toolkit/content/tests/browser/browser_saveImageURL.js
+++ b/toolkit/content/tests/browser/browser_saveImageURL.js
@@ -43,17 +43,17 @@ add_task(async function preferred_API() 
       saveImageURL(
         url,
         "image.jpg",
         null,
         true,
         false,
         null,
         null,
-        null,
+        "image/jpeg",
         null,
         false,
         gBrowser.contentPrincipal
       );
       await SpecialPowers.spawn(gBrowser.selectedBrowser, [], async () => {
         let channel = docShell.currentDocumentChannel;
         if (channel) {
           todo(
@@ -109,13 +109,23 @@ add_task(async function deprecated_API()
           // Throttleable is the only class flag assigned to downloads.
           todo(
             channel.QueryInterface(Ci.nsIClassOfService).classFlags ==
               Ci.nsIClassOfService.Throttleable
           );
         }
       });
       let filePickerPromise = waitForFilePicker();
-      saveImageURL(url, "image.jpg", null, true, false, null, doc, null, null);
+      saveImageURL(
+        url,
+        "image.jpg",
+        null,
+        true,
+        false,
+        null,
+        doc,
+        "image/jpeg",
+        null
+      );
       await filePickerPromise;
     }
   );
 });