Hi,

When we initially started, we did have a rough time but I haven't seen any
issue nor heard any negative feedback about it. As far as I can tell from
the metrics, it seems to save a lot of user frustration.

Iirc, we collected a bunch of cases where the feature behave erratically.
We had a form, an outreach, perhaps some url-keyed metrics and/or what-if
metrics, auto-disengaging thresholds (?) It was a long time ago, perhaps
Steve has a better memory than I.

Are these compat issues specific to Firefox, or do they also trigger weird
behaviors on Chrome? Do you have a sense of the size and convergence for
the problematic cases?

On Fri, Sep 27, 2019, 21:23 Emilio Cobos Álvarez <emi...@mozilla.com> wrote:

> Hi,
>
> (cc'ing webkit-dev@ and blink-dev@ in case they have feedback or
> opinions, as WebKit is the only engine which does not implement scroll
> anchoring, though I don't know if they plan to, and Blink is the only
> other engine that does implement it. Please reply to dev-platform@
> though.)
>
> TLDR: Scroll anchoring is really a mess.
>
> I didn't do the initial implementation of the feature in Gecko, but I've
> done a ton of work over the last few months to fix compat issues in our
> implementation (see all the bugs blocking [1]).
>
> At this point, our implementation is mostly compatible with Blink, but
> even with a bug-for-bug compatible implementation, we did get compat
> issues because of different content being served for different browsers,
> or because our anti-tracking protections changing the final content of
> the page slightly ([2] is an example of bug which only reproduces with
> ETP enabled only, but whose reduced test-case renders the site unusable
> in Chrome as well).
>
> If you hit one of the broken cases as a user you think the browser is
> completely broken, and the site is just unusable.
>
> I've fixed those by tweaking the heuristics Gecko uses. Those extra
> heuristics have also caused other compat issues, like [3], reported
> today, which will require other adjustments to the heuristics, etc...
>
> On top of that, the spec is not in a good state, with ton of open issues
> without feedback from the editors [4].
>
> So right now I'm at a stage where I think that the feature is just not
> worth it. It doesn't behave predictably enough for developers, and you
> have no guarantee of it behaving consistently unless you test a
> particular browser, with a particular content in a particular viewport
> size... That's not great given the current dominant position of
> Chromium-based browsers.
>
> On top, issues with scroll anchoring are pretty hard to diagnose unless
> you're aware of the feature.
>
> All in all, it doesn't seem like the kind of feature that benefits a
> diverse web (nor web developers for that matter), and I think we should
> remove the feature from Gecko.
>
> Does anyone have strong opinions against removing scroll anchoring from
> Gecko, based on the above?
>
> Thanks,
>
>   -- Emilio
>
> [1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1519644
> [2]: https://bugzilla.mozilla.org/show_bug.cgi?id=1561450
> [3]: https://bugzilla.mozilla.org/show_bug.cgi?id=1584499
> [4]: https://github.com/w3c/csswg-drafts/labels/css-scroll-anchoring-1
>
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>
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