I'm pretty sure ns* plugins for Firefox will also work perfectly in Chrome.
Chrome happens to load plugins from two locations: Firefox's plugin directory (yes, 'tis true), and its own - which is located in Chrome's Application data directory.
The location of Chrome's plugin directory is:
On XP: C:\Documents and Settings\<your_username>\Local Settings\Application Data\Google\Chrome\Application\Plugins\
On Vista/7: C:\Users\<your_username>\AppData\Google\Chrome\Application\Plugins\
If the 'Plugins' directory doesn't exist, you can simply create it and put your plugin in there instead.
And regarding that little popup thing that asks if you'd like to install an extension: That behavior is defined somewhere in Chrome's installation (used to be from a .xml file, but I think they stopped using it), so you can't use HTML to make that popup show-up that asks if you'd like to install the plugin.
Could you not, instead, somehow use Javascript to detect what plugins are currently loaded, and notify the user to install the plugin another way?
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NSAPI extensions in Chrome
