Andreas Farre
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Aug 26, 2026, 2:29:03 PMAug 26
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Jeff Muizelaar
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Aug 26, 2026, 3:26:07 PMAug 26
to Andreas Farre, dev-pl...@mozilla.org
It seems like this will break stuff on Nightly wherever Chrome currently has an origin trial. Can we get that list from them? Without that list, it seems like we're taking webcompat risk for limited gain.
-Jeff
Andreas Farre
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Aug 26, 2026, 4:40:20 PMAug 26
to Jeff Muizelaar, dev-pl...@mozilla.org
As far as I understand it XSLT has been disabled by default on Chrome
Canary, Dev, and Beta since December 2nd 2025, and their origin trial
scheduled to start yesterday. I'm not entirely sure this is what
actually happened, and I don't know if that means that they would
start running the origin trial on non-stable channels when it's been
turned off for so long. But looking at
https://developer.chrome.com/origintrials/#/view_trial/1902207892610613249
the starting version is indeed 152, which is the current release.
But just to be clear, are you suggesting that we should run our our
origin trial for Nightly only until we unship this in Aug 2028?
Andreas[2]
[1] https://developer.chrome.com/docs/web-platform/deprecating-xslt#timeline_for_chrome
correctly,
[2] Sorry Jeff for the double reply, I forgot reply all
Jeff Muizelaar
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Aug 26, 2026, 4:57:46 PMAug 26
to Andreas Farre, dev-pl...@mozilla.org
Are we running an origin trial?
Chrome's current disablement has presumably helped them build a list of origins currently broken with XSLT disabled. If we disable on Nightly, all of those sites will be broken and we'll have to discover them ourselves. If we can't get the list of sites that Chrome has left XSLT enabled, disabling it on Nightly has a clear webcompat cost and offers limited advantage.
So my suggestion is:
1. Copy the list of origins that Chrome has XSLT enabled and leave it enabled for those origins on Nightly
or
2. Don't disable on Nightly until Chrome's origin trial has ended (Aug 30, 2027)
-Jeff
Emma Zühlcke
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Aug 27, 2026, 12:23:36 PMAug 27
to Jeff Muizelaar, Andreas Farre, dev-pl...@mozilla.org
Isn't Nightly exactly the channel for trying out new configurations? What is our stance on webcompat in Nightly? I had the impression website breakage is acceptable on Nightly, especially given that this config will reach release "soon". For folks who are testing with Nightly this is an opportunity for them to spot breakage in their own applications.
Simon Pieters
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Aug 27, 2026, 3:28:59 PMAug 27
to Emma Zühlcke, Jeff Muizelaar, Andreas Farre, dev-pl...@mozilla.org
To clarify the Chromium timeline, their plan is to turn it off on Stable in 158, which is in November. I assume there are very few sites that have opted in to the origin trial, since it's new and it's still enabled in Stable.
I believe we can't get origin trial participants from them, but we can run a query in httparchive to find such pages (if they're in the dataset).
Apart from the origin trial, Chromium has re-enabled XSLT (temporarily) for CAP Alert documents. We could copy this for Nightly if we're worried about annoying Nightly users who view such documents.
--
Mason Freed
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Aug 29, 2026, 12:15:45 AMAug 29
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Thanks for this intent! I'm obviously supportive. To confirm a few things, Chromium disabled XSLT completely on all pre-stable channels in December of last year. And we launched the origin trial in 152, which went to stable this week. There are a few registrants, but really not many yet. I don't believe I can share the list, unfortunately, but I can probably share the rough scale of the list, if that's helpful. Today there are 15 registrants total.
The current plan is to turn it off by default in 158, which goes to stable around Nov 17. That's usually when the bulk of the origin trial registrations happen. Though I'm trying to land a user-visible banner on all XSLT sites in 154 (September), which might help.
Good luck with this!
Thanks,
Simon Pieters
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Sep 7, 2026, 1:58:52 PM (8 days ago) Sep 7
to Jeff Muizelaar, Andreas Farre, dev-pl...@mozilla.org
Are we running an origin trial?
Chrome's current disablement has presumably helped them build a list of origins currently broken with XSLT disabled. If we disable on Nightly, all of those sites will be broken and we'll have to discover them ourselves. If we can't get the list of sites that Chrome has left XSLT enabled, disabling it on Nightly has a clear webcompat cost and offers limited advantage.
I think the idea is to send a signal that we're serious about removing support, and give developers enough time to address any XSLT usage.
I'm not sure if removing support in Nightly will sufficiently reach developers, though. Maybe a user-visible message at the top of the page (for all users) is more effective? (Chrome now has such a message.)
So my suggestion is:
1. Copy the list of origins that Chrome has XSLT enabled and leave it enabled for those origins on Nightly
We can do this (for origins we can find in httparchive), but not until some time after November 17 (e.g. in Q1 2027).
or
2. Don't disable on Nightly until Chrome's origin trial has ended (Aug 30, 2027)
IMO we can be slightly more aggressive than this, but I agree we should generally avoid having an extended period of time of broken sites in Nightly while they continue to work in Chrome (due to origin trial or other).
cheers,