With Ubuntu 14.10 64-bit (Intel® 965GM) there seems to be scrolling lag in WebKitGtk library (libwebkit2gtk-3.0-25 version: 2.4.6-1ubuntu1) in website play.google.com/music I tested it in WebKit2Gtk MiniBrowser: /usr/lib/x86_64-linux-gnu/webkit2gtk-3.0/libexec/MiniBrowser http://play.google.com/music With Ubuntu 14.04 64-bit(ATI HD3850) (libwebkit2gtk-3.0-25 version: 2.4.4-1ubuntu1) scrolling this website is okey.
I'm very interested in this issue because it affects my WebKitGtk-based application Nuvola Player that runs Google Play Music website to integrate the web app with desktop environments. However, I cannot reproduce it on any of my devel machines, but M can :-) I've only noticed that the Google Play Music website doesn't load with the experimental VirtualBox 3D-capable driver, but loads fine once the VirtualBox 3D support is disabled. Can be the M's lag issue GPU related? What steps should M take to provide you with more useful information? Thank you :-)
Setting LIBGL_DRI3_DISABLE=1 to disable DRI3 can be used as a workaround for now.