Midi plug-in for OS 10.8.5?

Question

Since upgrading my iMac to 10.8.5, I am unable to play midi files because of Missing Plug-in.  What do I need to do to restore midi files? 

Answer 1

This works for me on 10.8.5 and 10.9 - although I haven't tested exhaustively & of course it's possible that there may be problems. It's easy to revert - just quit any browsers & remove the plug-in file added below. It's all within the User folder, no admin access required.
I copied a QuickTime Plugin.plugin from Snow Leopard to the Home/Library/Internet Plug-Ins folder & renamed it QuickTime Plugin2.plugin.
Ctrl-click on that 'new' file & choose 'show package contents'... open the 'Contents' folder & edit the file 'info.plist' (Textedit works, but the file must not be saved as rich text).
Change the keys : CFBundleName, CFBundleIdentifier and WebPluginMIMETypesFilename - adding '2' after 'plugin' in each case. Save the file.
You then need to create a new file in Home/Library/Preferences named 'com.apple.quicktime.plugin2.preferences.plist'
I copied one from 10.6.8, then removed every mimetype except those for audio/mid & midi, which left the file looking like this : (hopefully this site won't mangle the formatting).
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
          <key>WebPluginLocalizationName</key>
          <string>en_US</string>
          <key>WebPluginMIMETypeFilteringVersion</key>
          <integer>1</integer>
          <key>WebPluginMIMETypes</key>
          <dict>
                    <key>audio/mid</key>
                    <dict>
                              <key>WebPluginExtensions</key>
                              <array>
                                        <string>mid</string>
                                        <string>midi</string>
                                        <string>smf</string>
                                        <string>kar</string>
                              </array>
                              <key>WebPluginTypeDescription</key>
                              <string>MIDI</string>
                              <key>WebPluginTypeEnabled</key>
                              <true/>
                    </dict>
                    <key>audio/midi</key>
                    <dict>
                              <key>WebPluginExtensions</key>
                              <array>
                                        <string>mid</string>
                                        <string>midi</string>
                                        <string>smf</string>
                                        <string>kar</string>
                              </array>
                              <key>WebPluginTypeDescription</key>
                              <string>MIDI</string>
                              <key>WebPluginTypeEnabled</key>
                              <true/>
                    </dict>
          </dict>
</dict>
</plist>
After saving the plist file, & restarting Safari - I have two Quicktime plug-ins shown in Safari - Help - Installed Plug-ins...
Opening a .mid file directly in the browser gives a warning & blocks it by default... choosing 'trust' plays the file as expected.
Visiting sites with embedded midi gives a similar per-site warning & choice...
choose Trust, & it loads & plays, just as on Snow Leopard...
anything other than mid/midi uses the newer plug-in - as shown below