Firefox cookie problems

I'm starting to notice multiple cloud apps that only work properly in a FireFox private window. In particular, a Looker custom visualization and AWS Quicksite. I looked at the Javascript console for both. For Looker, the Javascript console looks the same as Chrome. My looker example is pretty custom, so I say throw it under the bridge.

For AWS Quicksite I see:

Skipping device list refresh; not signed in 8 browser-sync.js:239:15

Unchecked lastError value: Error: Could not establish connection. Receiving end does not exist. background.js:31

NS_ERROR_FAILURE: Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIInterfaceRequestor.getInterface] network-response-listener.js:84

So, aside from clearing cookies or using a private window, any other suggestions? My hunch it is cookies from one specific location which is the culprit, but I'd rather not have to experiment to find what is.