1916778 - Video sometimes gets briefly displayed at top-left with white background before TopLevelVideoDocument resources load (flash of unstyled content)

Status: NEW

(Core :: Layout: Images, Video, and HTML Frames, defect)

Description

[Daniel Holbert [:dholbert]]

STR:

1. Visit https://bugzilla.mozilla.org/attachment.cgi?id=9422614&action=edit in a fresh profile.
2. Make your browser-window as large as possible, and set "Website appearance: dark" in Firefox preferences (these just make the bug easier to see)
3. Click "Download the attachment" (which actually just navigates to a video file) and as it loads, watch the top-left of your viewport very closely.
4. If the actual-results haven't yet appeared, navigate back and then clear your cache (ctr+shift+del or history|clear-recent-history)

ACTUAL RESULTS:
Occasionally there's a flash-of-unstyled-content when the video loads, where the TopLevelVideoDocument.css styling hasn't loaded yet, where:

• the video is snapped to the top left corner
• the page background is white instead of dark
• ...and then the page jumps to its final rendering with a centered video and a dark background.

EXPECTED RESULTS:
No such flash-of-unstyled-content. The video should be centered and shown over a dark background at its first rendering. The TopLevelVideoDocument css file is local, so there's no reason for there to be a delay in having those styles available.

Here's a profile showing this bug -- hover over the screenshots track to see the brief misrendering:
https://share.firefox.dev/3ZaKTsG

Here's the same profile zoomed in a bit further so you can see the misrendering a bit clearer in the screenshots track (the portion with a white background):
https://share.firefox.dev/3Xv8J11

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: low-res screenshot of the misrendering, taken from Firefox Profiler

Comment 2

[Daniel Holbert [:dholbert]]

Attachment: low-res screenshot of the expected rendering, taken from Firefox Profiler