1620347 - Two different full-screen behaviors when privacy.resistFingerprinting.letterboxing = true

Status: RESOLVED DUPLICATE of bug 1450401

(Core :: DOM: Security, defect, P3)

Description

[Brian Carpenter [:geeknik]]

Hi. I noticed there are 2 different fullscreen behaviors in Firefox Nightly (ASAN Build ID 20200305095541) on Fedora 31 with xfce4, Nvidia RTX 2070 and v440.64 drivers, but only when you have enabled privacy.resistFingerprinting and privacy.resistFingerprinting.letterboxing.

STR:

1. Set privacy.resistFingerprinting and privacy.resistFingerprinting.letterboxing to true. Restart as necessary.
2. Visit YouTube and start playing any video.
3. Tap F11 on the keyboard.
4. Notice the letterboxing around the fullscreen video.
5. Tap F11 to leave full screen, then tap the full screen icon in the YouTube player.
6. Notice the lack of letterboxing.

YouTube's Stats for nerds reports a viewport of 1477x831 for Theater mode, 1655x931 for F11, and 1920x1080 for YouTube Fullscreen. I'm on a 24" monitor with a native resolution of 1920x1200.

Comment 1

[Thorin [:thorin]]

(In reply to Brian Carpenter [:geeknik] from comment #0)

5. Tap F11 to leave full screen, then tap the full screen icon in the YouTube player.
6. Notice the lack of letterboxing.

Letterboxing does not apply to elements

• https://ghacksuserjs.github.io/TorZillaPrint/TorZillaPrint.html#screen <-- click here on the full screen test and it will return two measurements: screen and an element that uses all available space

Tor: https://trac.torproject.org/projects/tor/ticket/32713

tom: duplicate of bug 1450401 ?

---

I didn't bother to look at the stats for nerds or how they calculate those values, but 1920x1080 is 16/9 exactly and the other two are as close as possible to 16/9 (whereas your screen is actually 16/10) - so I suspect they're reporting possible video dimensions, not actual viewport/inner/screen measurements

Comment 2

[Tom Ritter [:tjr]]

Seems pretty close to a dupe, but I'm going to leave it open as something to double check if we get into a position to double check it.