Unfortunately the link provided
https://support.apple.com/kb/DL1321?locale=en_US does not offer the desired firmware MP51.0089.B00. Note the date on the linked page: Oct 28, 2010. It is just MP51.007F.B03 offered for download there. Apple does not offer MP51.0089.B00 as a separate download -- see its page
https://support.apple.com/en-us/101198 dated October 26, 2023. Probably the only way to upgrade the firmware to MP51.0089.B00 is in the process of making a High Sierra volume. So if, for some reaon, you only want the firmware without High Sierra make a High Sierra volume and erase it.
