A better solution would be decrypting the image and then loading the image into an image tag with a data: uri in base64 encoding.
I could zoom normally with the browsers own zoom tools, I could right-click save normally, etc.
The site is perfectly usable. More than usable, even, because I get RES-style zooming for free, amongst other things.
You can right-click save normally already - just right-click and save. If you want the browser zoom tools, hit the "View in Browser" button or right-click and open in new tab
This website works in every browser I've used, and I've never heard of any problem even remotely close to what you say you're running into.
You might say your browser works fine, but I'd put my money on something there being the issue.
Neither "Save as" nor "View in new tab" work.
I said so on the github issue, too
Do you have running app for mouse gestures? That's the only thing I can think of that makes sense in your scenario. Try holding the right click for a few seconds, see if the context menu appears.