So, I am 99% sure that r197062 fixed the screen tearing issue not just on GitHub, but also on various other sites, including http://blog.twshodgson.co.uk/2015/02/23/pandoc-beamer-template/ (middle click the "pandoc" tag directly underneath the title on that page, I get lots of screen tearing in 2.10.7 but not in 2.10.8 nor in trunk). So that's great. But I am still seeing screen tearing when loading pages on Julita's blog in new tabs (middle click on the heading "JHbuild, finally! :D" a bunch of times): https://lleksah.wordpress.com/2016/03/13/jhbuild-finally-d/ It looks almost the same as one form of the tearing that used to occur on GitHub. However, it's somehow a different issue, because the GitHub problem is almost certainly gone. With the tearing on Julita's blog, scrolling the page *does not* fix the screen tearing like it does on the sites fixed by r197062. Instead, the tearing sometimes goes away once the page is fully loaded, but sometimes, if the page is fully loaded, I think it gets stuck until I switch tabs. If the page is not fully-loaded, then switching tabs usually does not remove the tearing, i.e. the tearing disappears when switching to an unaffected tab, but returns when returning to an affected tab.
Hm. I notice that the page https://www.python.org/dev/peps/ is sometimes affected by this screen tearing. (Scrolling the page *does* fix the screen tearing in this case.) It was reportedly broken by the fix for bug #126122. Loading that page many times in separate tabs in an attempt to reproduce the tearing, my entire desktop hung; hence, I recommend not attempting to reproduce on that site. This indicates that the pages still affected by screen tearing are probably related to the set of pages affected by bug #126122.