Here's what I did to reproduce the bug: I copied the th-TH.dic and th-TH.aff files from your attachment to firefoxdir/dictionaries, and I tried using the locale switcher add-on, and I couldn't reproduce the crash.
amai: can you find the XPI file that contains those dictionaries so that we can install them as a normal add-on?
Here's what I did to reproduce the bug: I copied the th-TH.dic and th-TH.aff files from your attachment to firefoxdir/ dictionaries, and I tried using the locale switcher add-on, and I couldn't reproduce the crash.
amai: can you find the XPI file that contains those dictionaries so that we can install them as a normal add-on?