1793782 - Cookie banner detection/clicking can fail if the banner shows up late due to slow load

Status: RESOLVED FIXED

(Core :: Privacy: Anti-Tracking, defect, P2)

Description

[Paul Zühlcke [:pbz]]

We currently run our cookie banner detection code on DOMContentLoaded. If we can't find a visible cookie banner element at that point, we will register a MutationObserver to observe DOM changes within the next 5 seconds until giving up.
This behavior is problematic for cases where the total site load takes longer than 5 seconds and the banner shows up late, e.g. because it depends on a subresource. In this case we will fail to handle the banner.

We can address this issue by registering the MutationObserver on DOMContentLoaded and unregistering it only after the load event. That is, starting the unregister-timeout when we observe the load event.

There may still be edge cases where banner show up after our default timeout of 5 seconds, even after page load. I'm considering this out of scope for this bug.

Comment 1

[Paul Zühlcke [:pbz]]

Attachment: Bug 1793782 - Extend MutationObserver lifetime to after page 'load' event. r=timhuang!

Comment 2

[Paul Zühlcke [:pbz]]

Attachment: Bug 1793782 - Add a test page that shows a cookie banner shortly after a slow page load. r=timhuang!

Depends on D159386

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/a26c89a3b18d
Extend MutationObserver lifetime to after page 'load' event. r=timhuang
https://hg.mozilla.org/integration/autoland/rev/7f8e72f11548
Add a test page that shows a cookie banner shortly after a slow page load. r=timhuang

Comment 4

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/a26c89a3b18d
https://hg.mozilla.org/mozilla-central/rev/7f8e72f11548