pkg/52535: firefox is crashy and it's gtk3's fault (broken icon theme)

[coypu%sdf.org@localhost]

>Number:         52535
>Category:       pkg
>Synopsis:       firefox is crashy and it's gtk3's fault (broken icon theme)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Sep 09 22:35:00 +0000 2017
>Originator:     coypu
>Release:        NetBSD 8.0_BETA
>Organization:
>Environment:
NetBSD localhost 8.0_BETA NetBSD 8.0_BETA (GENERIC.201709060310Z) amd64

>Description:
Firefox crashes a lot for me so I ran it in gdb and got this backtrace.
I got it from trying to save a file in my home directory in firefox.

Thread 1 received signal SIGSEGV, Segmentation fault.
0x0000000058a0536c in mozalloc_abort(char const*) ()
(gdb) bt
#0  0x0000000058a0536c in mozalloc_abort(char const*) ()
#1  0x0000000058a05336 in abort ()
#2  0x00007aca8826752e in g_assertion_message () from /usr/pkg/lib/libglib-2.0.so.0
#3  0x00007aca882675ac in g_assertion_message_expr () from /usr/pkg/lib/libglib-2.0.so.0
#4  0x00007aca933d6ff9 in ensure_surface_for_gicon () from /usr/pkg/lib/libgtk-3.so.0
#5  0x00007aca933d7654 in gtk_icon_helper_load_surface () from /usr/pkg/lib/libgtk-3.so.0
#6  0x00007aca933d771c in gtk_icon_helper_ensure_surface.part () from /usr/pkg/lib/libgtk-3.so.0
#7  0x00007aca933d78ce in _gtk_icon_helper_get_size () from /usr/pkg/lib/libgtk-3.so.0
#8  0x00007aca933e94d0 in gtk_image_get_content_size () from /usr/pkg/lib/libgtk-3.so.0
#9  0x00007aca9335c3f7 in gtk_css_custom_gadget_get_preferred_size () from /usr/pkg/lib/libgtk-3.so.0

...
literally 140 frames in total

Looking at gtk, it has only one assert in the function:
  if (destination == NULL)
    {
      destination = gtk_icon_theme_load_icon (icon_theme,
                                              "image-missing",
                                              width,
                                              flags | GTK_ICON_LOOKUP_USE_BUILTIN | GTK_ICON_LOOKUP_GENERIC_FALLBACK,
                                              NULL);
      /* We include this image as resource, so we always have it available or
       * the icontheme code is broken */
      g_assert (destination);
      symbolic = FALSE;


I must be missing the icon "image-missing" so it asserts. not sure how it happened, but it probably shouldn't.
>How-To-Repeat:

>Fix:
??? gtk3