I now suspect this problem is not in Firefox after all, as it is now sometimes taking the whole system down rather than just Firefox (a common pattern is for X to suddenly restart for no apparent reason, get as far as logging in then restart again, and keep repeating this until X decides something is wrong and waits, at which point all I can do is restart the system; more rarely error messages appear that look like log messages but don't actually make it to the system logs, the only set I managed to cut and paste before the system went down being included below), and sometimes applications other than Firefox crash. I suspect this is really either an anti-virus software problem (I have also reported it to Sophos) or a kernel/driver/hardware compatibility problem, or possibly a hardware fault though it doesn't seem to affect Win98; please move it to wherever you think is appropriate. I am also having video problems (https://launchpad.net/bugs/82434), though since they are new in Ubuntu while this problem was also present in Debian I suspect they are a separate problem. Hardware as reported by Device Manager: CS 4614/22/24 [CrystalClear SoundFusion Audio Accelerator] Realtek RT8139 network card Allied Data Technologies Unknown (0x0015) (I think this is my modem, which I don't use) Intel 82371AB/EB/MB PIIX4 ISA Intel 82371AB/EB/MB PIIX4 IDE HDS728080PLAT20 (Primary master, partitioned approx 40GB FAT32 Win98 boot/0.5GB Swap/40GB ext3 Ubuntu boot) ST36421A (Secondary master, approx 6GB FAT32) OPTOWRITECD-RW CW5205 (Secondary slave) Intel 82371AB/EB/MB PIIX4 USB Intel 82371AB/EB/MB PIIX4 ACPI (Power management is turned off in Services but I still get an "ACPI: Unable to locate RSDP" error followed by a "GConf schema installer error, battery_low_percentage cannot be zero" on every startup) Intel 440LX/EX - 82443LX/EX Host bridge Intel 440LX/EX - 82443LX/EX AGP bridge ATI 3D Rage Pro Turbo AGP 2X graphics Mouse, floppy drive, UK keyboard This is consistent with Win98's identification. Memory 256MB, processor 500MHz Celeron. The following errors occurred on closing gdb after Firefox had run successfully; I then attempted to reboot the system but it went to a black screen with a text cursor, and on pressing Ctrl-Alt-Del showed "init:process rc6 (number) killed by signal 15", went to the Ubuntu screen with the progress bar stopped at 2-3 blocks from the end, then went back to the blank screen. Program exited normally. (gdb) quit Message from syslogd@mert1529 at Thu Jan 11 16:52:13 2007 ... mert1529 kernel: [32929.412974] ------------[ cut here ]------------ Message from syslogd@mert1529 at Thu Jan 11 16:52:13 2007 ... mert1529 kernel: [32929.413008] kernel BUG at mm/rmap.c:560! Message from syslogd@mert1529 at Thu Jan 11 16:52:13 2007 ... mert1529 kernel: [32929.413018] invalid opcode: 0000 [#1] Message from syslogd@mert1529 at Thu Jan 11 16:52:13 2007 ... mert1529 kernel: [32929.413025] SMP Message from syslogd@mert1529 at Thu Jan 11 16:52:13 2007 ... mert1529 kernel: [32929.413210] CPU: 0 Message from syslogd@mert1529 at Thu Jan 11 16:52:13 2007 ... mert1529 kernel: [32929.413274] EIP is at page_remove_rmap+0x27/0x40 Message from syslogd@mert1529 at Thu Jan 11 16:52:13 2007 ... mert1529 kernel: [32929.413288] eax: ffffffff ebx: c2bc2a04 ecx: cb2b287c edx: c118b540 Message from syslogd@mert1529 at Thu Jan 11 16:52:13 2007 ... mert1529 kernel: [32929.413302] esi: c118b540 edi: b4a81000 ebp: 00000000 esp: c5415ed8 Message from syslogd@mert1529 at Thu Jan 11 16:52:13 2007 ... mert1529 kernel: [32929.413313] ds: 007b es: 007b ss: 0068 Message from syslogd@mert1529 at Thu Jan 11 16:52:13 2007 ... mert1529 kernel: [32929.413325] Process gdb (pid: 5066, threadinfo=c5414000 task=cdb52a90) Message from syslogd@mert1529 at Thu Jan 11 16:52:14 2007 ... mert1529 kernel: [32929.413334] Stack: c0158446 00000000 cde8d43c c5415f44 00148000 00000000 00000001 b4c00000 Message from syslogd@mert1529 at Thu Jan 11 16:52:14 2007 ... mert1529 kernel: [32929.413362] c59f3b48 c77093c0 c12035e0 fffffffd ffffffff c105784c c59f3b48 b708afff Message from syslogd@mert1529 at Thu Jan 11 16:52:14 2007 ... mert1529 kernel: [32929.413390] b708b000 00000000 c5415f44 c6d85f94 c77093c0 00000001 c015b3ce ffffffff Message from syslogd@mert1529 at Thu Jan 11 16:52:14 2007 ... mert1529 kernel: [32929.413417] Call Trace: Message from syslogd@mert1529 at Thu Jan 11 16:52:14 2007 ... mert1529 kernel: [32929.413425] unmap_vmas+0x2a6/0x570 exit_mmap+0x7e/0x100 Message from syslogd@mert1529 at Thu Jan 11 16:52:14 2007 ... mert1529 kernel: [32929.413544] mmput+0x33/0xa0 do_exit+0xe2/0x840 Message from syslogd@mert1529 at Thu Jan 11 16:52:14 2007 ... mert1529 kernel: [32929.413613] do_page_fault+0x3db/0x6f0 do_group_exit+0x37/0x80 Message from syslogd@mert1529 at Thu Jan 11 16:52:14 2007 ... mert1529 kernel: [32929.413695] sysenter_past_esp+0x54/0x79 Message from syslogd@mert1529 at Thu Jan 11 16:52:14 2007 ... mert1529 kernel: [32929.413759] Code: 00 00 00 00 89 c2 90 83 40 08 ff 0f 98 c0 84 c0 75 02 f3 c3 8b 42 08 83 c0 01 78 0f ba ff ff ff ff b8 10 00 00 00 e9 c9 12 ff ff <0f> 0b 30 02 08 5f 2f c0 eb e7 eb 0d 90 90 90 90 90 90 90 90 90 Message from syslogd@mert1529 at Thu Jan 11 16:52:14 2007 ... mert1529 kernel: [32929.413875] EIP: [page_remove_rmap+39/64] page_remove_rmap+0x27/0x40 SS:ESP 0068:c5415ed8