From what I gather, users will need to keep IE11 or FF ESR v52 loaded on a PC that will be backwards compatible for users with the model cameras listed in this thread. Going forward, from what I'm told, D-Link will not be making these model cameras compatible with newer versions of browsers or OS. The NPAPI based add-ons are what all newer browsers no longer support. These and the cameras FW would need to be updated on many levels.
Users may need to look into newer model cameras that are more supportive of newer browsers and OS systems if there older cameras are not working or accessible thru browsers and the portal.
Good Luck.