Nice extension! I tried it.
Testing is
- WindowsXP Firefox1.5.0.1
1. Add the search engine normally. (Name contains Japanese letters.)
2. Use the search with some Japanese words.
IS08859-1... needless to say 
 
Shift_JIS... OK! 
 
EUC_JP... Great! 

 (similar to EUC_KR?)
UTF-8... ( 
http://zh.openoffice.org )
an error shown on clicking "Finish":
引用:
an error occured while converting.
some characters might be replaced by "?"
What the error say occurs. Japanese letters becomes ????
Recentdays, number of UTF-8 pages are increasing. Support if you can please. 
P.S. It willbe better that added searches are usable without restarting 
