"Bus error" with Thunderbird: Crash log says: EXC_BAD_ACCESS (0x0001)

I wanted to try out Thunderbird and experienced the following: Everything works fine, until I try to write, forward or reply to a mail or want to change the "Compose"-Button in Thunderbird preferences.

In mozillazine they can't help anymore because they don't have enought Mac-expertise for the stuff. They are quite sure, however, that it's an interoperability problem caused by some other application which doesn't know what it's doing... But: How to identify the culprit?

So, here we go: While Terminal just says bus error, the problem report is as follows:

Date/Time: 2009-05-29 13:50:17.755 +0200
OS Version: 10.4.11 (Build 8S165)
Report Version: 4

Command: thunderbird-bin
Path: /Applications/Thunderbird.app/Contents/MacOS/thunderbird-bin
Parent: WindowServer [57]

Version: 2.0.0.21 (2.0.0.21)

PID: 162
Thread: 0

Exception: EXC BADACCESS (0x0001)
Code[0]: 0x0000000a
Code[1]: 0x0e0cd000


Thread 0 Crashed:
0 <<00000000>> 0xffff8a4c __memcpy + 684 (cpu_capabilities.h:189)
1 ATS 0x9676c524 GetDataFontFragment + 120
2 ATS 0x9676c5c0 FTDataForkReadTableBytes(privateFontObjectRecord const*, sfntDirectoryEntry*, unsigned long, unsigned long, void*) + 120
3 ATS 0x9678b058 _eFOReadTableBytes + 192
4 ATS 0x9678af68 _eFOGetFontTable + 124
5 ATS 0x9678aec8 FOGetFontTable + 112
6 com.apple.QD 0x9f5a90e4 FMGetFontTable + 76
7 org.mozilla.thunderbird 0x0089661c

It of course goes on like this forever but I can't read that stuff and don't know what you might need to figure out the problem.

And here's the problem discussion in mozillazine: http://forums.mozillazine.org/viewtopic.php?f=39&t=1270145&p=6586775

Any ideas?!