PlayerPrefs doesn't save in WebGL

I made a tiny project and it proves it out. It has a single text input field and all it does is load and save to PlayerPrefs. It works fine in editor and on standalone builds.

Project files: https://drive.google.com/open?id=14IEXDxoynwUtpRbaf9Mljzr0g0E1_bbP

However:
- Exporting to WebGL with 2018.2.12f1 the application works as expected;
- But exporting to WebGL with 2019.1.0b5 the application does not work -- it fails to save to PlayerPrefs.

(when it works I can see /idbfs with key-value pairs in Application > Storage > IndexedDB. When it doesn't work /idbfs is not created. Interestingly /idbfs-test is always there, and so is UnityCache.)

I tested the WebGL applications with FF and Chrome.

...help, please? We need PlayerPrefs for a lot of player account and device preferences persistence. Hopefully there's a workaround? We've already updated to 2019.1 a while back and I'm not sure how destructive the process of going back would be.

Update: just tried with 2019.2.0a9 and it doesn't work either. The "/idbfs" database isn't even created. I tried creating it by hand to see if the application would save to it but no dice.

 

Sure, here it is: Case 1140820

Thanks!