The following tests times out sometimes (not very often) on GTK, since long ago. imported/w3c/web-platform-tests/mathml/relations/css-styling/color-1.html The bots suggest there is stderr, but the link is broken: https://build.webkit.org/results/GTK%20Linux%2064-bit%20Release%20(Tests)/r233504%20(7268)/imported/w3c/web-platform-tests/mathml/relations/css-styling/color-1-stderr.txt