1526874 - Initial page load might not be handled despite blocking Webrequest Listener

Status: NEW

(WebExtensions :: Request Handling, defect, P3)

Description

[Jan Henning [:JanH]]

STR on Android:

1. Install an extension using a blocking WebRequest listener, e.g. https://bugzilla.mozilla.org/attachment.cgi?id=9041271 (or simply uBlock Origin if you've already got it installed).
2. Back out the fix for bug 1496684.
3. Make sure Firefox isn't running (swipe away all instances in the task switcher and/or force stop it).
4. Launch a custom tab or a PWA [1] (i.e. something that doesn't launch the normal, full browser UI).

Expected:
Because of bug 1496684, extension startup never completes and all network connections covered by the extension's manifest should be held indefinitely through the persistent startup listener mechanism.

Actual:
Depending on the device, the initial page load might in fact come through and load successfully before the extension kicks in. This might in fact be inversely related to the device speed:

• On the ARM emulator (very slooooow), I can not only get the initial page load to complete normally, but even manage to navigate by clicking a link or two before the extension starts loading and blocks all further loads.
• On my real device (Moto G4 Play), the initial page load likewise completes normally, but subsequently clicking any links doesn't work.
• However we've also had enough reports for bug 1496684 where people couldn't load any pages at all in custom tabs/PWAs, i.e. the extension would load fast enough to catch even the initial load.

[1] I.e. something for which you've added a home screen short cut through the corresponding button from the URL bar - if you need some example page, probably try looking at https://pwa.rocks/.