T - some in-product Firefox links don't redirect to English (en-US) page if localized version doesn't exist

[Archaeopteryx]

Summary
some in-product Firefox links don't redirect to English (en-US) page if localized version doesn't exist

Steps To Reproduce (STR)
How can we reproduce the problem?

1. Get a localized Firefox Nightly (79.0a1) or Beta (78.0b3). Reproduced this with German (de) and French (fr).
2. Open https://www.mozilla.org
3. Press Shift + F9 to open the web storage inspector.
4. In the left sidebar, click onto a category, e.g. 'Indexed DB'.
5. In the main pane, a text with a link will be shown. Click the linl.

Actual behavior
https://developer.mozilla.org/Tools/Storage_Inspector/IndexedDB gets opened but MDN claims the page doesn't exist.

Expected behavior
English content opened: https://developer.mozilla.org/en-US/docs/Tools/Storage_Inspector/IndexedDB

Additional context
This works e.g. for HTTP headers (tested with German):

1. Press Ctrl+Shift+E to open the net monitor.
2. Load a page, e.g. https://www.mozilla.org/de/
3. Click onto the initial request.
4. In the right sidebar, go to the line with "x-xss-protection".
5. Click the button with the question mark.
   Actual & expected result: https://developer.mozilla.org/de/docs/Web/HTTP/Headers/X-XSS-Protection?utm_source=mozilla&utm_medium=devtools-netmonitor&utm_campaign=default opened with English content (see dropdown with available languages at the top right - it's a fallback and not a German page with the English content manually pasted).

Does the fallback only work e.g. for /Web/ pages?

[peterbe]

You can reproduce this with this command:

curl -I -H "accept-language:de" https://developer.mozilla.org/Tools/Storage_Inspector/IndexedDB

Somewhere in kuma it says "This user wants German" but it never checks if that page has been translated so it's not using the usual fallback functionality that kicks in if you go to https://developer.mozilla.org/de/docs/Tools/Storage_Inspector/IndexedDB
However, that page is a bit messed up in that the HTTP exit code is actually 404 but it proceeds to display the en-US document (with a German chrome).

I think the solution should be; if you have a Accept-Language header that leads to a failed docment lookup-by-locale, it should do a redirect to the fallback if the URL doesn't have the /$locale/docs/ prefix. That's going to be something we need to care for and solve in Yari too.

[atopal]

Dev tools should link to a URL that has /docs in it

[tobinmori]

action: notify FF devtools to update link

@atopal do you know who to contact for this?

[atopal]

I filed an issue for this in the devtools repo: firefox-devtools/devtools-core#1206

[nchevobbe]

filed https://bugzilla.mozilla.org/show_bug.cgi?id=1655957 for the storage inspector

[juliandescottes]

This was fixed in https://bugzilla.mozilla.org/show_bug.cgi?id=1646945 and was uplifted all the way up to FF78