Decrypt ~/Library/Safari/Form Values file or force Safari to autofill?

I've run into a problem that seems to have cropped up after the last Safari update.

I have a Netgear switch that has a login page with just a password field. In the past I was able to log in to it using a saved password, which Safari would auto-fill from the Other Forms list.

However, now when I try, all Safari does is give me an option to suggest a new password 😟. This is Safari 11.0.2 (13604.4.7.1.3) running on OS X 10.13.2.

I've spent a couple of hours trying to find a way to decrypt the file, but basically everything I can find points to a site that used to have an OS X app to decrypt the file, but now only has a windows app that is encoded in EnPack, which doesn't appear to have a free extractor.

Anyone have pointers on how to get Safari to auto-fill this page, or how to decrypt the file? Otherwise I have to wipe out the config on the switch in order to reset the password, and that's something I really don't want to do.

Thanks.