Description of problem:
The problem was encountered in the normal use of Web. I did have several tabs open at the time. I do not know of any way to reproduce the bug.

Version-Release number of selected component:
epiphany-runtime-3.14.2-3.fc21

Additional info:
reporter:       libreport-2.3.0
backtrace_rating: 4
cmdline:        epiphany
crash_function: _gtk_css_value_equal
executable:     /usr/bin/epiphany
kernel:         3.17.6-300.fc21.x86_64
runlevel:       N 5
type:           CCpp
uid:            1000

Truncated backtrace:
Thread no. 1 (9 frames)
 #0 _gtk_css_value_equal at gtkcssvalue.c:119
 #1 _gtk_css_computed_values_get_difference at gtkcsscomputedvalues.c:272
 #2 _gtk_style_context_validate at gtkstylecontext.c:3077
 #5 gtk_container_idle_sizer at gtkcontainer.c:1738
 #6 _g_closure_invoke_va at gclosure.c:831
 #8 g_signal_emit_by_name at gsignal.c:3405
 #9 gdk_frame_clock_paint_idle at gdkframeclockidle.c:408
 #15 g_main_context_iteration at gmain.c:3842
 #16 g_application_run at gapplication.c:2282