Here are screen shots.

...and it turns out it's an Apple plug-in. doh.

http://www.macuser.de/forum/thema/687783-Plugin-Default-Browser-Helper-537-seit-OSX-10-9

That's from Apple, comes with the 10.9 update.

thanks for the quick reply.

I don't know too much German - but the page referenced, I believe, is just repeating what was said here...Apple needs to describe this app on an Apple site/page - I'm also not certain, but anyone can fake a copyright line in an App (can't they?) - there's so much that's suspicious about this plugin - there is more than one space before the number "537" in the name of the plugin - no documentation from Apple - I've cleaned up numerous friend's computers and usually it's some lurking plugin that is the source of all kinds of trouble with browsing and efficient computer use...this is a big "fail" for Apple - they need to keep us informed.

I used Mac Universal Translator and this is what I got from this link: http://www.macuser.de/forum/thema/687783-Plugin-Default-Browser-Helper-537-seit-OSX-10-9

Translated:

Since upgrading to Mavericks I have a new plugin in my Firefox browser. The "Default Browser Helper 537". Is at the same plug you suddenly appeared, or does anyone know why (and what) this plugin is needed?

According to the plugin "more" info, its a plugin that tracks your default browser, as if it were Apple's business to know how I use my computer. I just turn it deactivated it and so much for Apple's usual arrogance.

The plug-in is used to promote the Safari web browser as the default browser. Specifically, the pug-in can open the attached dialog from within any web browser. The user must visit a web site that has very specific content to trigger the dialog. The plug-in cannot execute without being called into action by visiting an [Apple] web site.

You techy guys who like your Firefox’s can safely disable the plug-in or even remove it from your systems.