When starting FF on my SNB laptop (with default page set to ecosia.org) I hit the following assertion: 

Program received signal SIGABRT, Aborted.
0x00000035b9e35819 in __GI_raise (sig=sig@entry=6)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
56	  return INLINE_SYSCALL (tgkill, 3, pid, selftid, sig);
(gdb) bt full
#0  0x00000035b9e35819 in __GI_raise (sig=sig@entry=6)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
        resultvar = 0
        pid = 11429
        selftid = 11429
#1  0x00000035b9e36f28 in __GI_abort () at abort.c:90
        save_stage = 2
        act = {__sigaction_handler = {sa_handler = 0x7fff5c047fa8, 
            sa_sigaction = 0x7fff5c047fa8}, sa_mask = {__val = {230753281033, 
              139747212314062, 341, 4294967295, 230751928629, 4, 
              140734737179744, 22, 140734737180656, 47244640288, 0, 0, 0, 
              21474836480, 139747222487040, 230753293032}}, 
          sa_flags = 1861404272, 
          sa_restorer = 0x7f196ef32190 <__PRETTY_FUNCTION__.25009>}
        sigs = {__val = {32, 0 <repeats 15 times>}}
#2  0x00000035b9e2e7f6 in __assert_fail_base (
    fmt=0x35b9f7d2e8 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", 
    assertion=assertion@entry=0x7f196ef2c670 "(((uintptr_t)(priv->gpu_damage))&1)", file=file@entry=0x7f196ef2c5ce "sna_accel.c", line=line@entry=341, 
    function=function@entry=0x7f196ef32190 <__PRETTY_FUNCTION__.25009> "assert_pixmap_damage") at assert.c:92
        str = 0x1ce5c60 ""
        total = 4096
#3  0x00000035b9e2e8a2 in __GI___assert_fail (
    assertion=0x7f196ef2c670 "(((uintptr_t)(priv->gpu_damage))&1)", 
    file=0x7f196ef2c5ce "sna_accel.c", line=341, 
    function=0x7f196ef32190 <__PRETTY_FUNCTION__.25009> "assert_pixmap_damage")
    at assert.c:101
No locals.
#4  0x00007f196ee03891 in assert_pixmap_damage (p=0x1ce5bb0) at sna_accel.c:341
        priv = 0x1ce9690
        reg = {extents = {x1 = 26112, y1 = 23556, x2 = 32767, y2 = 0}, 
          data = 0x7f196ee02d57 <to_sna_from_pixmap+38>}
        cpu = {extents = {x1 = 13920, y1 = 28440, x2 = 32537, y2 = 0}, 
          data = 0x1ce5bd0}
        gpu = {extents = {x1 = 26080, y1 = 23556, x2 = 32767, y2 = 0}, 
          data = 0x1ce0488}
        __PRETTY_FUNCTION__ = "assert_pixmap_damage"
#5  0x00007f196ee09aac in sna_drawable_move_region_to_cpu (drawable=0x1ce5bb0, 
    region=0x7fff5c046830, flags=1) at sna_accel.c:2228
        pixmap = 0x1ce5bb0
        sna = 0x7f196d548000
        priv = 0x7fff5c046860
        dx = 23556
        dy = 26432
        __FUNCTION__ = "sna_drawable_move_region_to_cpu"
        __PRETTY_FUNCTION__ = "sna_drawable_move_region_to_cpu"
#6  0x00007f196ee10083 in sna_put_zpixmap_blt (drawable=0x1ce5bb0, 
    gc=0x1cdd430, region=0x7fff5c046830, x=0, y=0, w=60, h=22, 
    bits=0x7f196b717028 "~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377"..., stride=240)
    at sna_accel.c:4058
        pixmap = 0x1ce5bb0
        box = 0x7f196ee01589 <RegionTranslate+38>
        dx = 0
        dy = 0
        n = 0
        __FUNCTION__ = "sna_put_zpixmap_blt"
        __PRETTY_FUNCTION__ = "sna_put_zpixmap_blt"
#7  0x00007f196ee11697 in sna_put_image (drawable=0x1ce5bb0, gc=0x1cdd430, 
    depth=24, x=0, y=0, w=60, h=22, left=0, format=2, 
    bits=0x7f196b717028 "~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377"...)
    at sna_accel.c:4433
        pixmap = 0x1ce5bb0
        sna = 0x7f196d548000
        priv = 0x1ce9690
        region = {extents = {x1 = 0, y1 = 0, x2 = 60, y2 = 22}, data = 0x0}
        dx = 0
        dy = 0
        __FUNCTION__ = "sna_put_image"
#8  0x0000000000433cd9 in ProcPutImage (client=0x1cbe080) at dispatch.c:1966
        pGC = 0x1cdd430
        pDraw = 0x1ce5bb0
        length = <optimized out>
        lengthProto = <optimized out>
        tmpImage = 0x7f196b717028 "~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377~D)\377"...
        stuff = 0x7f196b717010
#9  0x0000000000436df7 in Dispatch () at dispatch.c:432
        clientReady = 0x1a55830
        result = <optimized out>
        client = 0x1cbe080
        nready = 0
        icheck = 0x814330 <checkForInput>
        start_tick = 560
#10 0x00000000004263fa in main (argc=8, argv=0x7fff5c046a68, 
    envp=<optimized out>) at main.c:298
        i = <optimized out>
        alwaysCheckForInput = {0, 1}