STR (1) Load https://mail.mozilla.com (2) Go to inbox (3) Pinch-zoom out very slowly At the right side of the screen, there's a flickering strip of unpainted content. If you do this very carefully, you can zoom out a little bit, stay at a constant zoom level, then pan left/right to see the unpainted strip appear and disappear. It appears to have three states: (i) fully painted; (ii) 1-pixel gray border; (iii) 2-pixel white border. My guess would be a rounding error in our GL code somewhere.
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