Remote config throws error in Firefox private browsing mode

[kenkus-futurice]

Describe your environment

• Operating System version: Windows 10
• Browser version: Firefox 70.0.1 private mode
• Firebase SDK version: 7.4.0
• Firebase Product: remote config

Describe the problem

Remote config throws error in Firefox (possibly also related problem in IE 11 and Edge) private browsing mode.

Error: Remote Config: Error thrown when opening storage. Original error: A mutation operation was attempted on a database that did not allow mutations.. (remoteconfig/storage-open).

Steps to reproduce:

Load a web app that uses remote config in Firefox private browsing mode.

Relevant Code:

import * as firebase from 'firebase/app';
import 'firebase/remote-config';

const remoteConfig = firebase.remoteConfig();

remoteConfig.settings = {
  minimumFetchIntervalMillis: 3600000,
};

remoteConfig.fetchAndActivate()
  .then(() => {
    doSomething();
  })
  .catch((err) => {
    console.error(err);
  });

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[rommelpe]

Thanks for your report. I was able to replicate this. I'll confirm internally to see if this is an intended behavior or bug (b/144839642), and I'll let you know once I have an update.

[kenkus-futurice]

I forgot to mention that it works fine in Chrome private mode.

[Feiyang1]

According to https://bugzilla.mozilla.org/show_bug.cgi?id=781982, indexeddb doesn't work in Firefox private mode and Remote config needs it to work.

The good news is that Firefox is working on enabling indexeddb in the private mode - https://bugzilla.mozilla.org/show_bug.cgi?id=1562669.

For now, if you have any way to detect the private mode, I'd suggest to do that and NOT initialize remote config if private mode is detected.

I will close the issue for now.

[kenkus-futurice]

Alright, probably then similar reason with IE11/Edge private mode.

Another problem is that this promise doesn't return anything when the error occurs:

firebase.remoteConfig().fetchAndActivate()
    .then((res) => {
      // This is not printed
      console.log(res)
    })
    .catch((err) => {
      // This is not printed
      console.error(err)
    })
    .finally(() => {
      // This is not printed
      console.log('finally')
    })

Is there some other way of "handling" this error?

[Feiyang1]

Ah, good catch! Once #2381 is merged and released, you will be able to catch the error.

For now, are you able to detect the private mode and not initiate RC at all?

[kenkus-futurice]

Thank you. Great news that you have already fixed this.
Probably I can do something (in IE11/Edge window.indexedDB seems to be null, in Firefox there are some hacks e.g. based on IndexedDB, but if I understood correctly the general direction is to make the browser APIs work also in private mode and make it harder to detect private mode in web apps) but perhaps I can wait until this fix is released.