So I have been wanting to ask for long time about this feature as my Axis cameras have this after doing a Firmware Update there is a place holder for the older UPDATE to be restored if you find you don't like the new UPDATE... Now there is some catches to this and that is if you Do a Factory Reset (Restore) then your backup of the older FW is no longer in your cameras info to restore back to. While I can't say that it goes away 100% because I have never asked Axis about it after a Reset. There might be a way to still access that after just isn't something that is showing on the WebUI after a Reset..
So what it would do, After installing a new FW, If you don't like it there is a Tab in the FW update area that you just click to Restore the old FW back to the camera and don't have to ask by a Ticket to Revert back.
Last Firmware Restore.
Last Firmware Restore.
Be Safe.