You can determine if your CPU supports sse2 with this command:
tux@slitaz:~$ cat /proc/cpuinfo | grep -o sse2
sse2
sse2
If yes it will output sse2 for each core of your cpu.
Remove broken thunderbird-17.0.11esr from repos.
tazpkg remove thunderbird
Install new package thunderbird-bin-60.6.1 :
tazpkg -gi thunderbird-bin
Thunderbird-bin is mozilla built binary packaged for slitaz.
Because it is not built from source and linked to slitaz libraries it shouldn't break when slitaz libraries are updated. Similar to firefox-official it has a built-in updater so it doesn't need to be updated by re-installing a newer version from slitaz repo.
Block it in tazpkg so it doesn't nag you to update.
tazpkg block thunderbird-bin
If your cpu doesn't support sse2 I packaged and posted links to mozilla builds of thunderbird-17.0.11esr and firefox-17.0.11esr that will run here:
http://forum.slitaz.org/topic/thunderbird-and-firefox-broken#post-47449