Two Plugin Problems

I get this when I try to build Demo. My OS is Win7 64bit, and my Firefox is in C:\Program Files (x86)\Mozilla Firefox\plugins. Maybe that's why it fail, but I don't know how to deal with it.

错误    8    error MSB3073: 命令“copy /Y "D:\Code Lib\JUCE\extras\browser plugin demo\build\win32\Debug\JuceBrowserPluginDemo.dll" "C:\Program Files\Mozilla Firefox\plugins"
:VCEnd”已退出,代码为 1。    C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\Microsoft.CppCommon.targets    113    6    JuceBrowserPluginDemo

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I copy "JuceBrowserPluginDemo.dll" to there manually. But It's Ok when I use IE to open test.html, Chrome is Ok, but Firefox is not, I need your help!