Do tests to determine whether to use workaround for binary data instead of relying on version number.

src/platform/CrossOrigin.coffee

@@ -11,6 +11,45 @@ eventPageRequest = do ->
 <% } %>
 CrossOrigin =
   binary: (url, cb, headers={}) ->
+    <% if (type === 'crx') { %>
+    CrossOrigin.binary2 url, cb, headers
+    <% } %>
+    <% if (type === 'userscript') { %>
+    CrossOrigin.test ->
+      CrossOrigin.binary2 url, cb, headers
+    <% } %>
+
+  <% if (type === 'userscript') { %>
+  # Test whether responseType 'arraybuffer' is supported
+  # If not, use overrideMimeType workaround (less efficient)
+  test: (cb) ->
+    return cb() if CrossOrigin.workaround?
+    CrossOrigin.workaround = true
+    try
+      if GM?.xmlHttpRequest
+        CrossOrigin.workaround = false
+        return cb()
+      GM_xmlhttpRequest {
+        method: 'GET'
+        url: 'data:,0'
+        responseType: 'arraybuffer'
+        onload: (xhr) ->
+          try
+            CrossOrigin.workaround = !(
+              !!xhr and
+              xhr.response instanceof ArrayBuffer and
+              (a = new Uint8Array(xhr.response)).length is 1 and
+              a[0] is 0x30
+            )
+          finally
+            cb()
+        onerror: cb
+      }
+    catch
+      cb()
+  <% } %>
+
+  binary2: (url, cb, headers) ->
     # XXX https://forums.lanik.us/viewtopic.php?f=64&t=24173&p=78310
     url = url.replace /^((?:https?:)?\/\/(?:\w+\.)?4c(?:ha|d)n\.org)\/adv\//, '$1//adv/'
     <% if (type === 'crx') { %>
@@ -19,10 +58,7 @@ CrossOrigin =
       cb response, responseHeaderString
     <% } %>
     <% if (type === 'userscript') { %>
-    # Use workaround for binary data in Greasemonkey versions < 3.2, in Pale Moon for all GM versions, and in JS Blocker (Safari).
-    workaround = $.engine is 'gecko' and GM_info? and /^[0-2]\.|^3\.[01](?!\d)/.test(GM_info.version)
-    workaround or= /PaleMoon\//.test(navigator.userAgent)
-    workaround or= GM_info?.script?.includeJSB?
+    {workaround} = CrossOrigin
     options =
       method: "GET"
       url: url