How to Fix Firefox “Unable to Access” DSM Web on macOS

by Rian

If you are having trouble connecting to Synology DSM via web with recent influx of Firefox and macOS updates, this is likely the cause. The odd bit of it all is that in my case, it didn’t happen after an update. I didn’t get any updates on either one, it just happened out of the blue. Many tips I found on DSM often recommended creating a certificate or look into Firefox’s certificate related settings, but I didn’t have my NAS set to be exposed to WAN; if I am only using it locally —with VPN, you don’t need external access—, I wasn’t planning to create a 90-day free certificate.

Symptoms

I am assuming Synology DSM is operational and DSM web is still reachable with other browsers. In my case, I could still reach DSM through Safari but not on Firefox. On Firefox, it didn’t give me much of error messages other than “unable to access”.

What’s even more surprising is that Firefox can still reach external websites. Only the DSM, and possibly the other local devices are unreachable, even with the https off.

Solutions

This is actually a macOS glitch, I believe. Open System Preferences, and navigate to Privacy & Security > Local Network. Try turning off and on Firefox from the list.

All the other apps that needed to either renew the permission actually had a popup message saying so, so I suspect something went haywire between the two. I will update the post if I find more on it.