Safari "opens" DMG / ZIP files instead of downloading them

Hi all --

I just got a new MacBook Pro, and my user account is transferred from a Time Machine backup of my old iMac G5. I'm attempting to install Google Chrome, but whenever I try to download files through Safari or Firefox, they both don't actually download the DMG file upon clicking the "Agree and download" button -- instead, they "open" the DMG file in the browser window, with its location URL in the URL field, and nothing else happens.

I've seen previous questions on this topic where the suggestion was to delete the Safari plist from the Caches folder in the Library -- but I just checked, and there isn't a Safari plist file in my Caches folder, for some reason. Speed Download used to be installed on this account, but when I started having this problem, I deleted it with AppZapper. No change; the problem continues.

Does anybody else have any other suggestions? I can download DMG files just fine if there's a plain HTML link to their location (I just right-click the link and save the file), but if there's a radio button to click, I can't do anything.