Not sure what exactly is going on here, but I think we're probably triggering the snapshot update at the wrong time. Also, I think this is a regression.

STR: 0. enable "Ctrl+Tab cycles through tabs in recently used order" in a new profile 1. open a new tab 2. accel+click on the "Mozilla Developer Network" tile 3. press ctrl+tab and keep ctrl pressed while MDN is loading -> the thumbnail updates a few times while the page is loading but the final image is all black This only happens with e10s.

I can reproduce this on Mac 10.11 with Nightly 51.0a1, 20160817030202. When was this feature introduced? I'll dig up a regression range.

(In reply to Tracy Walker [:tracy] from comment #2) > When was this feature introduced? It's been around for a long time but behind a hidden pref: browser.ctrlTab.previews

Mark 51 as fix-optional by P3.

Any progress here, Tracy?

The regression range is nearly 2 years ago. I wasn't able to use mozregression to track this down. mozregression wasn't fully respecting prefs set to make sure this is reproducible. builds with mozregression were not displaying suggested site tiles. So a manual one day regression range was all I could dig up. last good build: 20150122030202 first buggy build: 20150123030203 This is a polish bug. The black tile persist only for the duration of holding ctrl in step 3. If you release ctrl and retrigger (ctrl+tab) the tab preview and the previously black thumbnail correctly contains a content preview.

(In reply to Tracy Walker [:tracy] from comment #6) > The regression range is nearly 2 years ago. I wasn't able to use > mozregression to track this down. mozregression wasn't fully respecting > prefs set to make sure this is reproducible. builds with mozregression were > not displaying suggested site tiles. So a manual one day regression range > was all I could dig up. > > last good build: 20150122030202 > first buggy build: 20150123030203 > > This is a polish bug. The black tile persist only for the duration of > holding ctrl in step 3. If you release ctrl and retrigger (ctrl+tab) the > tab preview and the previously black thumbnail correctly contains a content > preview. Based on that, maybe bug 1088203? Dão, does that help?

(Looking at https://hg.mozilla.org/mozilla-central/pushloghtml?startdate=2015-01-22&enddate=2015-01-23, fwiw, which might not be entirely accurate... revisions would be better than dates, but it's late - I can look again if comment 7 is a terrible guess and we need a more accurate pushlog to keep looking)

(In reply to :Gijs from comment #7) > Based on that, maybe bug 1088203? Dão, does that help? Quite possible. Bug 1088203 adds async messages, changing the timing around when exactly we'd take a screenshot and perhaps exposing a race condition. The underlying issue that we get a black thumbnail when taking the screenshot at the "wrong" time is likely older and not a bug in front-end code.

Non-default behaviour => fix-optional.

Pushed by shughes@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/d6e93c10a90d Update ctrlTab thumbnails asynchronously. r=dao