1615954 - YouTube and other sites don't switch to mobile mode when in Responsive Design Mode

Status: NEW

(DevTools :: Responsive Design Mode, defect, P2)

Description

[fireattack [:fireattack]]

User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.106 Safari/537.36

Steps to reproduce:

1. Open DevTool, enable enter Responsive Design Mode, and enable "Touch Simulation".

2. Open https://youtube.com or https://ameblo.jp/aya21-0921/entry-12575350548.html

Actual results:

It opens up a desktop version.

Expected results:

It should redirects to the mobile interface.

---

These are just two websites I found today. I've encountered other websites that don't show mobile version with touch simulation enabled before.

Comment 1

[fireattack [:fireattack]]

Attachment: 001.png

Actually, it causes problem on this very page..

Comment 2

[fireattack [:fireattack]]

Attachment: 002.png

With "Touch Simulation" disabled, page shows in mobile mode just fine.

Comment 3

[Brad Werth [:bradwerth]]

The Touch Simulation button also triggers the interpretation of the site's meta viewport tag. With this mode on, if there is no meta viewport tag, we interpret the page as having a desired 980px wide layout viewport, scaled to fit the width of the simulated device. With this mode off, the site is laid out in whatever width the simulated window actually is, and most sites will use media queries to control how much content they attempt to present with the limited space.

In the YouTube case, www.youtube.com delivers a site with no meta viewport tag, but m.youtube.com has a meta viewport tag. If you navigate to m.youtube.com, you'll see that the site appears correct whether or not Touch Simulation is turned on. So the real issue here is that YouTube is not delivering the m.youtube.com site when in Firefox Responsive Design Mode.

ameblo.jp is doing something similar where the site doesn't deliver a meta viewport tag to Firefox for some reason, but does deliver it to Chrome.

bugzilla.mozilla.org has a viewport tag specifying a width of 1024 and is working as intended, and behaves similarly in Chrome's device simulation mode.

So this bug is about how servers are detecting if Firefox Responsive Design Mode is a "real" mobile device and what criteria they use. RDM is not triggering the desired response. This could be due to User Agent string detection on the server.

Comment 4

[fireattack [:fireattack]]

Thanks for your investigation.

Comment 5

[Micah [:mtigley] (she/her)]

Could also be related to Bug 1595017