Description of problem:
The crash happened while watching a youtube flash in full-screen, inside Firefox.
Mouse was still moveable but no interaction was possible from the GUI and the keyboard did no respond.
Connection from another computer via ssh was possible and I rebooted the system from there.

Additional info:
reporter:       libreport-2.2.3
WARNING: CPU: 1 PID: 1176 at drivers/gpu/drm/i915/intel_display.c:3361 intel_crtc_wait_for_pending_flips+0x1a5/0x1b0 [i915]()
Modules linked in: tcp_lp fuse ipt_MASQUERADE xt_CHECKSUM tun nf_conntrack_ftp ip6t_rpfilter cfg80211 ip6t_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw ppdev parport_pc eeepc_wmi asus_wmi sparse_keymap snd_hda_codec_realtek snd_hda_codec_hdmi snd_hda_codec_generic rfkill tpm_infineon tpm_tis iTCO_wdt parport iTCO_vendor_support snd_hda_intel snd_hda_controller snd_hda_codec snd_hwdep serio_raw snd_seq x86_pkg_temp_thermal snd_seq_device snd_pcm coretemp snd_timer kvm_intel i2c_i801 kvm e1000e shpchp ptp pps_core tpm wmi snd crct10dif_pclmul crc32_pclmul mei_me mei crc32c_intel lpc_ich mfd_core ghash_clmulni_intel soundcore microcode joydev raid1 i915 i2c_algo_bit drm_kms_helper drm video
CPU: 1 PID: 1176 Comm: Xorg Not tainted 3.17.7-200.fc20.x86_64 #1
Hardware name: ASUS All Series/Q87M-E, BIOS 0906 11/28/2013
 0000000000000000 00000000ad9570be ffff8807e6403a58 ffffffff8172758c
 0000000000000000 ffff8807e6403a90 ffffffff81092e7d 0000000000000000
 ffff8807f3819000 ffff8807ef9d82c0 ffff8807f0686000 0000000000000000
Call Trace:
 [<ffffffff8172758c>] dump_stack+0x45/0x56
 [<ffffffff81092e7d>] warn_slowpath_common+0x7d/0xa0
 [<ffffffff81092faa>] warn_slowpath_null+0x1a/0x20
 [<ffffffffa00db7b5>] intel_crtc_wait_for_pending_flips+0x1a5/0x1b0 [i915]
 [<ffffffff810d1840>] ? prepare_to_wait_event+0xf0/0xf0
 [<ffffffffa00e2c44>] intel_crtc_disable_planes+0x34/0x160 [i915]
 [<ffffffffa00e3b65>] haswell_crtc_disable+0x55/0x330 [i915]
 [<ffffffffa00dd4e8>] __intel_set_mode+0x2c8/0x1610 [i915]
 [<ffffffff8128ef04>] ? ext4_dirty_inode+0x54/0x60
 [<ffffffffa00e6076>] intel_set_mode+0x16/0x30 [i915]
 [<ffffffffa00e702c>] intel_crtc_set_config+0x92c/0xe60 [i915]
 [<ffffffffa001d584>] drm_mode_set_config_internal+0x64/0xf0 [drm]
 [<ffffffffa001eee1>] drm_framebuffer_remove+0x101/0x160 [drm]
 [<ffffffffa0022388>] drm_mode_rmfb+0xd8/0x100 [drm]
 [<ffffffffa0013e0c>] drm_ioctl+0x1ec/0x660 [drm]
 [<ffffffff81215cb5>] ? __d_free+0x35/0x40
 [<ffffffff81215cfd>] ? dentry_free+0x3d/0x60
 [<ffffffff81216c9c>] ? __dentry_kill+0x14c/0x1c0
 [<ffffffff81213500>] do_vfs_ioctl+0x2e0/0x4a0
 [<ffffffff81213741>] SyS_ioctl+0x81/0xa0
 [<ffffffff8112f426>] ? __audit_syscall_exit+0x1f6/0x2a0
 [<ffffffff8172ec69>] system_call_fastpath+0x16/0x1b