J&P Group > J&P InfoSol > Applications > Firefox Web Browser > Development
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A couple of extracts from http://www.undermyhat.org/blog/2009/09/tip-how-to-unpack-xpi-files/:
Extracting XPI
To extract or unpack the XPI, you can rename the file to *.ZIP and open it in your favorite unzip tool. Internally, just like a JAR file, an XPI is basically nothing more than a PKZip compatible archive which you can view and modify using any ZIP utility.
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Some other information on XPI
If your web server also serves XPI files, it must do so with the MIME type application/x-xpinstall.
A valid XPI archive starts with the hexadecimal values 0×50 0×4B 0×03 0×04. A damaged or corrupted file can sometimes be recovered by unzip utilities like WinZip or WinRar. An XPI file contains executable code. Do not install a plugin if you don’t trust the site where you got it from.