Adding to the browser user agent string?

Question

I have a plug-in that handles its own url schema (something like mystuf:// ). If a user clicks on such a link when the plug-in isn't installed (s)he gets an ugly error. So I extended my installer to write into the Registry (for Internet Explorer) and the user.js (for Firefox) to ADD a custom string to the user agent string. These additions survive a browser upgrade nicely (Microsoft uses this technique to indicate the presence of the dotNet Framework).

Now I need to extend this to Apple Safari and Google Chrome on all supported platforms.

To be clear: I'm not looking how to REPLACE the user agent string, but how to amend it with additional information.

Any hint?

Answer 1

As Google Chrome supports the Netscape Plugin API ( http://en.wikipedia.org/wiki/NPAPI ), the Firefox way might be a good starting point also there.

Answer 2

I faced a similar problem and I implemented this in the same way as apple do for iTunes as described in this SO question. Finding information on how to create the Firefox plugin was more tricky, but the answer to my question was a great help. The Firefox (or mozilla) plugin will be used by all mozilla based browsers (Firefox, Chrome, Safari) and you will therefore be able to use the same javascript to detect the firefox plugin in all of these browsers and therefore determine whether your plugin/custom protocol/application is installed.