window.find dialog feature broken in Firefox 53 (a.k.a., Late Intent to Unship: window.find's dialog support)

[Mike Conley]

Hello release-drivers (with dev-platform cc'd),

TL;DR: The non-standard window.find feature[1] has, historically, been
able to open up a dialog for the user to enter more strings to find on
the page[2]. It turns out that the dialog portion of that API has been
broken for all users with e10s enabled since e10s started shipping.
Starting with Firefox 53, we're breaking the dialog portion of the API
for non-e10s users as well. In bug 1348409[3], I have a patch cooking
that will disable the dialog functionality in a more deliberate way.

Longer version:

It appears that either bug 1182569 or bug 1232432 (or both) have broken
the part of the non-standard window.find API that can show a dialog to
the user, and that this breakage is about to go out in Firefox 53.

It also turns out that dialog feature has _never_ been supported with
e10s enabled.

The fact that we're only finding this out now says something about our
test coverage for this feature.

If it's any solace though, our documentation[1] spells it out pretty
clearly that this is a non-standard API, and that support varies widely
across browsers. My own testing indicates that the dialog is not shown
for IE 11, Edge, Safari 10.1, or Chrome 57 (on OS X). I have no idea if
they ever supported it in the past. IE and Edge don't seem to have
window.find support in general.

I have a patch cooking in bug 1348409 that disables the attempt at
opening the dialog. I'll go one of two ways - either returning false
from window.find as soon as we enter the case where we would have opened
a dialog, or just ignoring the dialog request entirely (this is what
Blink / WebKit seem to do, and what I'm leaning towards).

Anyhow, just a heads up. I hope I didn't ruin anybody's day.

-Mike

[1]: https://developer.mozilla.org/en-US/docs/Web/API/Window/find
[2]: http://www.javascripter.net/faq/find_dia.htm has a demo you can try
[3]: https://bugzilla.mozilla.org/show_bug.cgi?id=1348409

[Liz Henry (:lizzard)]

Just a quick note that I'm not going to consider this a release blocker for
53. We don't think this is commonly used API, and it is non-standard.

We can think about it as a fix to include for a potential 53 dot release a
couple of weeks from now.

Best,

Liz

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--
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Liz Henry (:lizzard)
Firefox Release Manager
lhe...@mozilla.com