24 May 10 13:39
So [Safari] must have Adobe Reader built in.
FireFox 3.6.3 apparently does not have Adobe Reader built in
Let's make this complicated.
Any browser (including Safari, Firefox, Opera, IE, Chrome) can be configured to open PDF files or to download them. A web server can also be configured to force download a PDF file instead of having the browser open it.
Adobe Reader is not the only PDF viewer. You can view PDF files in OS X without Adobe Reader. These browsers can have various helper apps associated to open/view PDF files. None of these browsers have built-in PDF capabilities. A helper app is always required.
Recognizing that every user will have a distinct configuration for handling PDF files, there is no reliable way to control how your end user will handle the file.
If the issue of being unable to access links within a PDF file is happening exclusively on your own computer, consider configuring Safari to use the Adobe Reader component instead of OS X Preview. The sample link to lacity.org works fine in my Safari because I have Adobe Reader assigned to view it within the browser.
It would help to troubleshoot this further if we knew what version of OS X was in use and if you were fully patched. I recall this issue in the past for OS X Preview and assumed it was already fixed.