https://icosahedron.website/media/4wjZq8aHPambTHTW4AU

The showing things happens only when I'm in Inspector -- normally it's black, although it started off-white, changing slightly when I scrolled up or down.

I say "Random", but actually the different spots it shows are 100% consistent based on which element I'm Inspecting, I think.

And changing the DOM does change it -- my internet connection dropped in the middle of trying to load the Github page (note that it DID start loading, according to the DOM), and when it showed the Github content it had different patterns of what showed.

Hmm, Screenshot Node seems to be behaving 100% normally.

https://icosahedron.website/media/x33V9aH0LnzuKLyVoe0

So I guess I don't need to worry about security issues, then. This seems to be just a display thing.

Oh hey it happened to multiple of my tabs. Including one that was already 100% loaded. HUH.

One of them only partially. It renders the glitching stuff UNDERNEATH one of the elements already existing:

https://icosahedron.website/media/kjsnmlEVLsacK7J6Umk

(The Blue Bar is from the original page. http://centrumlumina.tumblr.com/post/63208278796/ao3-census-masterpost )

Okay so I think I've poked at this as best I could, I need to prep for Shabbat. If anyone has something they want me to try, I'll check back in a bit, but like.

(Echt, sure I'll also keep my computer open, on and plugged in in the closet over Shabbat so I don't risk messing with it. So if any Mozillans or like people-who-have-any-idea-how-browser-rendering-works come by or anything, give me stuff to do and look at.)

OH! Yeah, 64bit GNU/Linux. I can give more specific specs when like actually filing an actual bug report and stuff and not just live-tooting it.

(Obviously though computers are chaotic systems so like it could resolve itself by motzei shobbos...)

@gaditb Any chance it's the video card? Also, I'd love to know whether you can steal images of (chunks of) previous tabs by using the Canvas screenshotting feature.

@varx Maybe? But it's notably only pulling stuff from other tabs, in the same window -- would a bug in the video card be able to consistently recognize process boundaries?

I checked for Screenshot Node (above), and it showed the correctly-rendered thing (despite not showing it to ME), so I don't think there are those security issues.

@gaditb Oh yeah, so you did! I wonder if that does the same thing as the canvas method (does it respect same-origin restrictions?)... but it does point to it not being an issue.

@gaditb OK, I was misremembering. thought there was something similar to https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/drawWindow that could be used from inside a page context, with the restriction that if any of the elements within the capture were other-origin, the canvas would be tainted.