can't install weblock.xpi

Hi to everybody who wants to help me!
I have briefly read the article "Creating XPCOM Components" and
downloaded the source code from: http://www.brownhen.com/weblock
Unfortunately I was not able to install the "weblock.xpi" file. Does I
make an obviously mistake?
I installed the xpi file by drag and drop the file to my Mozilla
Browser. The Software Installation Window opened and also the
installation was successful, but when I started the Mozilla Browser
again, the Icon "weblock" in the status line did not occur. How can I
activate the weblock component?
I really appreciate every help!!!