Regarding the firmware, D-Link usually posts firmware as a zip file which is a standard file format. I'm sure there are tools (either native to the Mac) or third party that can expand the archive. There are quite a number of Mac users who own these cameras and this has never come up as an issue, at least on this forum.
If this function is not natively available in your OS, then there are plenty of free third party alternatives you can download (e.g. Stuffit Expander, etc.).