Go to youtube.com, start playing any video, and repeatedly enter and then exit fullscreen mode. Eventually, WebKit will start printing a warning spam on the command line: Failed to get GBM buffer from swap chain: no buffers available Failed to get GBM buffer from swap chain: no buffers available Failed to get GBM buffer from swap chain: no buffers available Failed to get GBM buffer from swap chain: no buffers available Failed to get GBM buffer from swap chain: no buffers available I remember Carlos Garcia mentioned he was confused as to why this error sometimes happened. Well, now we have a reproducer. :)
This also happens when entering and exiting fullscreen mode on reddit.com videos.