It would appear if a customer is using Communities or force.com sites there is no way to build scalable custom object URL buttons that work everywhere.

Let's say on the Account object you have a custom URL button that opens a Visualforce page with the following text:

/apex/findNearby?id={!Account.Id}

In this example we can't make the Content Source of the button Visualforce as this findNearby.page does not use a standard controller or extension.

For a normal user inside salesforce.com this works fine but let's say an org has a Community named 'customers'. This is were things start to break. That link should then redirect to:

/customers/apex/findNearby?id={!Account.Id}

So you might be thinking, no problem, just use the $Site global variable and do the following in the URL button:

{!URLFOR($Site.Prefix+'/apex/findNearby?id='+Account.Id)}.

This would normally work but here is the final caveat...this is part of a managed packaged that needs to support Group and Professional editions and in these editions the $Site var does not exists.

Unless I am missing something this seems to be a gap in functionality for creating URL button links with Communities.

Is there anyway, within a button to detect the correct url or salesforce version and build the appropriate URL?

Thanks,

Jason