I've been seeing these for a while now.

syslog (same in kern.log)

Jan  2 23:09:45 fox kernel: [47353.396349] show_signal_msg: 42 callbacks suppressed
Jan  2 23:09:45 fox kernel: [47353.396352] steamwebhelper[16791]: segfault at 0 ip 00000000f42307a0 sp 00000000ff880e40 error 4 in libcef.so[f32fe000+4019000]
Jan  2 23:09:53 fox kernel: [47361.585819] steamwebhelper[16819]: segfault at 0 ip 00000000f42307a0 sp 00000000ff880fb0 error 4 in libcef.so[f32fe000+4019000]

apport.log

:/var/log$ cat apport.log.1
ERROR: apport (pid 16818) Fri Jan  2 23:09:45 2015: called for pid 16791, signal 11, core limit 0
ERROR: apport (pid 16818) Fri Jan  2 23:09:45 2015: executable: /home/meh/.local/share/Steam/ubuntu12_32/steamwebhelper (command line "/home/meh/.local/share/Steam/ubuntu12_32/steamwebhelper\ --type=renderer\ --disable-accelerated-video-decode\ --disable-delegated-renderer\ --disable-gpu-compositing\ --disable-threaded-compositing\ --enable-pinch\ --enable-software-compositing\ --no-sandbox\ --lang=en-US\ --lang=en_US.UTF-8\ --product-version=Valve\ Steam\ Client\ --enable-pinch\ --disable-accelerated-compositing\ --channel=5151.5.1600223688")
ERROR: apport (pid 16818) Fri Jan  2 23:09:45 2015: executable does not belong to a package, ignoring
ERROR: apport (pid 16837) Fri Jan  2 23:09:53 2015: called for pid 16819, signal 11, core limit 0
ERROR: apport (pid 16837) Fri Jan  2 23:09:53 2015: executable: /home/meh/.local/share/Steam/ubuntu12_32/steamwebhelper (command line "/home/meh/.local/share/Steam/ubuntu12_32/steamwebhelper\ --type=renderer\ --disable-accelerated-video-decode\ --disable-delegated-renderer\ --disable-gpu-compositing\ --disable-threaded-compositing\ --enable-pinch\ --enable-software-compositing\ --no-sandbox\ --lang=en-US\ --lang=en_US.UTF-8\ --product-version=Valve\ Steam\ Client\ --enable-pinch\ --disable-accelerated-compositing\ --channel=5151.7.685453506")
ERROR: apport (pid 16837) Fri Jan  2 23:09:53 2015: executable does not belong to a package, ignoring

Not sure which other log may give more information... there aren't any steam logs in there, anyways. None of the files in ~/.local/share/Steam/logs/ show anything related.

I can't really force this problem and they seem to happen at random. But I'm pretty sure that when they do, the client becomes partially unresponsive. And anything flash (notably the videos) become nearly impossible to use. Most other pages, especially long ones, won't show me more than above the fold. Once you scroll down, the image gets "stuck". An artifact I used to see every now and then on the web which related to flash. Most pages that have this problem eventually lock up.

This affects all tabs except for the library ones. Switching to another tab allows me to restart the page, to at least see above the fold and until the problem happens again. A fresh restart of the client will allow me to use it as normal, but eventually the problem happens again. I have no reliable repro for it, yet.

Happy to do more research on it, it's been bothering me for one or two months, at least, now.

Fresh installation of Xubuntu 14.10, NVIDIA GK110B (GeForce GTX 780 Ti) with proprietary drivers. Beta steam client (although I've seen the problems before I switched to beta as well)