Recent updates to the OS as well as anti-virus programs have the ability to block .htc files, especially those that might provide cross-domain scripting. Since the viewer has the ability to have .htc files blocked, even if they don't know they now have that ability due to default settings, the viewer isn't going to benefit from the contents of that file anyway.
Taken from one of the paragraphs at the W3C, here's what a .htc file is capable of doing.
"Another possible use for HTCs is to provide cross-domain scripting access; the HTC could declare which properties, methods and events are allowed to be accessed from outside the domain."
So, if the viewer's browser is set to block this type of file, your efforts are being ignored.
The bottom line is, IF you've got JavaScript in a .htc file, consider putting it in an external .js file instead and forget otherwise trying to script the browser behavior.