It is likely there is an available plugin which belongs to Apple. However, I could not not find out any accurate information about it. What is “Default Browser Helper 537” firefox plugin? where to download it?
From my view, The Mavericks – OS X 10.9 introduces to users a new web browser plugin named “Default Browser Helper” to promote the Safari web browser as the default browser. The plug‐in is very simple. It only contains one test called
isSafariDefaultBrowser, and when it sees any other web browser it will open the below dialog. It is unclear when and where this is used.