Comment 139 for bug 1160569

I have the same problem, FreeBSD-10.1 amd64, fresh system install from scratch in VM, firefox-36.0.1, dwm window manager, G_SLICE workaround doesn't help, --safe-mode also doesn't help. FF prints the warning and freezes. No FF window opens.

It fails on xorg in VM, but same FF succeeds on Xnest in VM, and on my binary-identical host system.

I obtained xdpyinfo log in all three cases, see attachments:
firefox-hang-VM-in-xorg.txt : hangs on xorg in VM
firefox-fine-VM-in-xnest.txt : works fine on xnest in VM
firefox-fine-host.txt : works fine on xorg on host system

When I compare dpyinfo from xorg in host system (where ff works), and dpyinfo from xorg in VM system (where ff hangs), the main difference is that on host it has extra extensions NV-CONTROL, NV-GLX and XINERAMA. And on VM xorg it has SGI-GLX. I suspect this SGI-GLX causes ff to hang. Xnest server doesn't have any GLX, so it works too.

Someone from the development team should just reproduce it. I can tell you step by step how to do this with FreeBSD:
1. Download FreeBSD 10.1 amd64 disc1.iso
2. Install OS off that iso into VirtualBox VM with 3GB disk
3. Boot, and as root install all with the following command: pkg install firefox xorg xinit hal dbus dwm dmenu
4. Add these two lines into /etc/rc,conf: hald_enable="YES" / dbus_enable="YES"
5. As a regular user create file .xinitrc with "exec dwm" in it
6. Run startx, in dwm use Shift-Alt-Enter to open terminal
7. Run firefox and observe the problem

In all cases, working or not, it prints this warning:
(process:58625): GLib-CRITICAL **: g_slice_set_config: assertion 'sys_page_size == 0' failed

Hope this helps.