Bug 166328

I'm having the same problem, but "MOZ_DISABLE_PANGO=1 thunderbird" is only 
fixing it for a local copy of thunderbird.  I need to get my corporate email via
an X-remote session over ssh and thunderbird on the remote system still doesn't
work when started like this.   Both ends are uptodate Fedora Rawhide.

I suspect that the new /usr/bin/sort from coreutils-5.92-1.x86_64.rpm is
breaking something in fontconfig's font caching.

I am able to fix the thunderbird problem by:
    downgrading to coreutils-5.2.1-56
    reinstalling fontconfig-2.3.91 to rebuild its caches using "rpm -Uvh
--replacepkgs"

See also bug#172028 "sort breaks autofs"

I was able to fix the problem (and run firefox and thunderbird again) by just
running fc-cache -f -s as root which is the post-install script for fontconfig.
 I don't think this one has anything to do with sort; reinstalling fontconfig is
what made it work for John Ellson.

*** Bug 172500 has been marked as a duplicate of this bug. ***

I can't start firefox/thunderbird either after updating fontconfig.  Rolling
back to fontconfig-2.3.91.cvs20051031-1.x86_64.rpm fixes the problem.

Starting program: /usr/lib64/thunderbird-1.5/thunderbird-bin
[Thread debugging using libthread_db enabled]
[New Thread 46912502701712 (LWP 4876)]
[New Thread 1084229984 (LWP 4879)]
[New Thread 1094719840 (LWP 4880)]
[New Thread 1105209696 (LWP 4881)]
[New Thread 1115699552 (LWP 4882)]
[New Thread 1126189408 (LWP 4883)]
[New Thread 1136679264 (LWP 4884)]
Detaching after fork from child process 4885.

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 46912502701712 (LWP 4876)]
nsHTMLReflowState::CalcLineHeight (aPresContext=Variable "aPresContext" is not
available.
) at nsHTMLReflowState.cpp:2228
2228      aFontMetrics->GetNormalLineHeight(normalLineHeight);
(gdb) bt
#0  nsHTMLReflowState::CalcLineHeight (aPresContext=Variable "aPresContext" is
not available.
) at nsHTMLReflowState.cpp:2228
#1  0x00002aaab0f200dd in nsBlockReflowState (this=0x7fffffa0e970,
aReflowState=@0x7fffffa0ee80, aPresContext=0x109f080, aFrame=0x13bf248,
    aMetrics=@0x7fffffa0efec, aTopMarginRoot=0, aBottomMarginRoot=0) at
nsBlockReflowState.cpp:172
#2  0x00002aaab0f1d4f2 in nsBlockFrame::Reflow (this=0x13bf248,
aPresContext=0x134f050, aMetrics=@0x7fffffa0efec,
    aReflowState=@0x7fffffa0ee80, aStatus=@0x7fffffa0ef90) at nsBlockFrame.cpp:770
#3  0x00002aaab0f1f5f9 in nsBlockReflowContext::ReflowBlock
(this=0x7fffffa0ef90, aSpace=Variable "aSpace" is not available.
) at nsBlockReflowContext.cpp:605
#4  0x00002aaab0f1b9b2 in nsBlockFrame::ReflowBlockFrame (this=0x13bee10,
aState=@0x7fffffa0f390, aLine={mCurrent = 0x13cf6e8},
    aKeepReflowGoing=0x7fffffa0f104) at nsBlockFrame.cpp:3449
#5  0x00002aaab0f1bf93 in nsBlockFrame::ReflowLine (this=0x13bee10,
aState=@0x7fffffa0f390, aLine={mCurrent = 0x13cf6e8},
    aKeepReflowGoing=0x7fffffa0f31c, aDamageDirtyArea=1) at nsBlockFrame.cpp:2610
#6  0x00002aaab0f1c5d4 in nsBlockFrame::ReflowDirtyLines (this=0x13bee10,
aState=@0x7fffffa0f390, aTryPull=1) at nsBlockFrame.cpp:2262
#7  0x00002aaab0f1d6d7 in nsBlockFrame::Reflow (this=0x13bee10,
aPresContext=0x109f080, aMetrics=@0x7fffffa0f820,
    aReflowState=@0x7fffffa0f710, aStatus=@0x7fffffa0fa9c) at nsBlockFrame.cpp:902
#8  0x00002aaab0f245e5 in nsContainerFrame::ReflowChild (this=Variable "this" is
not available.
) at nsContainerFrame.cpp:904
#9  0x00002aaab0f39b3e in CanvasFrame::Reflow (this=0x138ff80,
aPresContext=0x109f080, aDesiredSize=@0x7fffffa0fb30,
    aReflowState=@0x7fffffa0f950, aStatus=@0x7fffffa0fa9c) at nsHTMLFrame.cpp:531
#10 0x00002aaab0f245e5 in nsContainerFrame::ReflowChild (this=Variable "this" is
not available.
) at nsContainerFrame.cpp:904
#11 0x00002aaab0f35bdf in nsHTMLScrollFrame::ReflowScrolledFrame
(this=0x13901c8, aState=Variable "aState" is not available.
) at nsGfxScrollFrame.cpp:515
#12 0x00002aaab0f35cd2 in nsHTMLScrollFrame::ReflowContents (this=0x13901c8,
aState=0x7fffffa0fbf0, aDesiredSize=@0x7fffffa10040)
    at nsGfxScrollFrame.cpp:570
#13 0x00002aaab0f37386 in nsHTMLScrollFrame::Reflow (this=0x13901c8,
aPresContext=Variable "aPresContext" is not available.
) at nsGfxScrollFrame.cpp:768
#14 0x00002aaab0f245e5 in nsContainerFrame::ReflowChild (this=Variable "this" is
not available.
) at nsContainerFrame.cpp:904
#15 0x00002aaab0f70d73 in ViewportFrame::Reflow (this=0x138fe80,
aPresContext=0x109f080, aDesiredSize=@0x7fffffa102a0,
    aReflowState=@0x7fffffa10110, aStatus=@0x7fffffa1024c) at
nsViewportFrame.cpp:239
#16 0x00002aaab0f03695 in IncrementalReflow::Dispatch (this=0x7fffffa102f0,
aPresContext=0x109f080, aDesiredSize=@0x7fffffa102a0,
    aMaxSize=@0x7fffffa102e0, aRendContext=@0x1381ef0) at nsPresShell.cpp:906
#17 0x00002aaab0f06eab in PresShell::ProcessReflowCommands (this=0x138eb10,
aInterruptible=1) at nsPresShell.cpp:6866
#18 0x00002aaab0f0f6f3 in ReflowEvent::HandleEvent (this=Variable "this" is not
available.
) at nsPresShell.cpp:6695
#19 0x00002aaaaae15962 in PL_HandleEvent (self=0x13d3690) at plevent.c:688
#20 0x00002aaaaae15d76 in PL_ProcessPendingEvents (self=0x5dca50) at plevent.c:623
#21 0x00000000006d0370 in ?? ()
#22 0x00002aaaaae1711f in nsEventQueueImpl::ProcessPendingEvents (this=0x130c)
at nsEventQueue.cpp:417
#23 0x00002aaaafa55067 in event_processor_callback (source=Variable "source" is
not available.
) at nsAppShell.cpp:67
#24 0x0000003b52225dde in IA__g_main_context_dispatch (context=0x54a780) at
gmain.c:1934
#25 0x0000003b52228aa5 in g_main_context_iterate (context=0x54a780, block=1,
dispatch=1, self=Variable "self" is not available.
) at gmain.c:2565
#26 0x0000003b52228f90 in IA__g_main_loop_run (loop=0xa1b170) at gmain.c:2769
#27 0x0000003b55b0c0c5 in IA__gtk_main () at gtkmain.c:985
#28 0x00002aaaafa553c6 in nsAppShell::Run (this=0x699a70) at nsAppShell.cpp:139
#29 0x00002aaab0048e0a in nsAppStartup::Run (this=0x6999f0) at nsAppStartup.cpp:150
#30 0x000000000040ccb8 in XRE_main (argc=-6224080, argv=0x7fffffa10850,
aAppData=0x2aaab06147da) at nsAppRunner.cpp:2313
#31 0x0000003b52d1cd2f in __libc_start_main () from /lib64/libc.so.6
#32 0x00000000004080c9 in _start ()
#33 0x00007fffffa10b78 in ?? ()
#34 0x0000000000000000 in ?? ()

After the Modular X update, thunderbird and firefox are working again with the
new fontconfig.

Based on last comment, closing this issue.