When loading http://technet.microsoft.com/en-us/sysinternals/bb897443.aspx with FireFox-11 (official build) on my i945GM, I hit the following assertion:

Program received signal SIGABRT, Aborted.
0x00dc9416 in __kernel_vsyscall ()
(gdb) bt
#0  0x00dc9416 in __kernel_vsyscall ()
#1  0x003e198f in __GI_raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#2  0x003e32d5 in __GI_abort () at abort.c:91
#3  0x003da6a5 in __assert_fail_base (
    fmt=0x51be48 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n",
    assertion=0xcc1dc0 "!must_tile(sna, pixmap->drawable.width, pixmap->drawable.height)", file=0xcc1a1e "sna_io.c", line=1091, function=0xcc1ea7 "indirect_replace")
    at assert.c:94
#4  0x003da757 in __GI___assert_fail (
    assertion=0xcc1dc0 "!must_tile(sna, pixmap->drawable.width, pixmap->drawable.height)", file=0xcc1a1e "sna_io.c", line=1091, function=0xcc1ea7 "indirect_replace")
    at assert.c:103
#5  0x00c34202 in indirect_replace (stride=76, src=0x8b64260, bo=0x8cced78,
    pixmap=0x8ccebb8, sna=0x87e3260) at sna_io.c:1089
#6  sna_replace (sna=0x87e3260, pixmap=0x8ccebb8, _bo=0x8cce984, src=0x8b64260,
    stride=76) at sna_io.c:1203
#7  0x00c0751b in sna_pixmap_move_to_gpu (pixmap=0x8ccebb8, flags=2)
    at sna_accel.c:2300
#8  0x00c08dcf in sna_pixmap_force_to_gpu (pixmap=0x8ccebb8, flags=2)
    at sna_accel.c:2172
---Type <return> to continue, or q <return> to quit---
#9  0x00c375c8 in sna_render_picture_partial (dst_y=91, dst_x=104, h=566, w=19, y=0,
    x=0, channel=0xbfcf6ccc, picture=0x8cced00, sna=0x87e3260) at sna_render.c:938
#10 sna_render_picture_extract (sna=0x87e3260, picture=0x8cced00, channel=0xbfcf6ccc,
    x=0, y=0, w=19, h=566, dst_x=104, dst_y=91) at sna_render.c:1039
#11 0x00c5a99c in gen3_composite_picture (sna=0x87e3260, picture=0x8cced00,
    op=0xbfcf6ca0, channel=0xbfcf6ccc, x=0, y=<optimized out>, w=19, h=566, dst_x=104,
    dst_y=91) at gen3_render.c:2372
#12 0x00c61d08 in gen3_render_composite (tmp=0xbfcf6ca0, height=566, width=19,
    dst_y=91, dst_x=104, mask_y=0, mask_x=0, src_y=<optimized out>, src_x=0,
    dst=0x8b31d18, mask=0x0, src=0x8cced00, op=3 '\003', sna=0x87e3260)
    at gen3_render.c:2815
#13 gen3_render_composite (sna=0x87e3260, op=3 '\003', src=0x8cced00, mask=0x0,
    dst=0x8b31d18, src_x=0, src_y=0, mask_x=0, mask_y=0, dst_x=104, dst_y=91,
    width=19, height=566, tmp=0xbfcf6ca0) at gen3_render.c:2733
#14 0x00c23d0e in sna_composite (op=3 '\003', src=0x8cced00, mask=0x0, dst=0x8b31d18,
    src_x=0, src_y=0, mask_x=0, mask_y=0, dst_x=104, dst_y=91, width=19, height=566)
    at sna_composite.c:488
#15 0x08156c3f in damageComposite (op=3 '\003', pSrc=0x8cced00, pMask=0x0,
    pDst=0x8b31d18, xSrc=0, ySrc=0, xMask=0, yMask=0, xDst=104, yDst=91, width=19,
    height=566) at damage.c:569
---Type <return> to continue, or q <return> to quit---
#16 0x081497db in CompositePicture (op=<optimized out>, pSrc=0x8cced00, pMask=0x0,
    pDst=0x8b31d18, xSrc=0, ySrc=0, xMask=0, yMask=0, xDst=104, yDst=91, width=19,
    height=566) at picture.c:1647
#17 0x0814ed9b in ProcRenderComposite (client=0x8ab95c0) at render.c:728
#18 0x0814a054 in ProcRenderDispatch (client=0x8ab95c0) at render.c:2063
#19 0x08076195 in Dispatch () at dispatch.c:439
#20 0x0806439a in main (argc=6, argv=0xbfcf7114, envp=0xbfcf7130) at main.c:287