[Firestore] Registering an unload listener and best practices

[dbstratta]

Describe your environment

• Operating System version: Ubuntu 20.10
• Browser version: Chrome 87.0.4280.88 (Official Build) (64-bit)
• Firebase SDK version: 8.2.1
• Firebase Product: firestore

Describe the problem

Lighthouse 6.4.0 on Chrome 87 warns that the firebase SDK registers an unload event listener and it can prevent browser optimizations like the Back-Forward Cache.

Steps to reproduce:

Enable the firestore local persistance.

Relevant Code:

import firebase from 'firebase/app';
import 'firebase/firestore';

firebase.firestore();
firebase.firestore().enablePersistence({ synchronizeTabs: true }); // Happens with `synchronizeTabs: false` too.

[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.

[wu-hui]

Thanks for the report! I believe this is something we should address, I can provide an update after the holidays, in the meantime, I'll keep the issue open.

[johanchouquet]

Hi @wu-hui,

I have the same issue. It brings our score in lighthouse to be not as high as it could be.

Did you plan to address that point in the end ?

[wu-hui]

Apologies for the long delay, this should be addressed in future releases.