[CentOS] firefox i386 1.5.0.5-0.el4.1.centos4

Hi all

I am using CentOS 4.3 and my default language is Japanese. I am using 
firefox with Japanese language. I installed firefox i386 
1.5.0.5-0.el4.1.centos4 update 15 M on my computer via yum yesterday. 
CentOS 4.3 has been acting strange! Japanese language on firefix has 
gone and English seems to be default language on firefox. I simply 
removed firefox 1.5.0.5-0.el4.1.centos4 and reinstalled firefox 
1.0.7-1.4.3.centos4, so I can use firefox with Japanese language. Would 
you know why this is happening? Is this happening only to me? I 
installed firefox extensions on firefox 1.0.7-1.4.3.centos4. Does it 
affect on firefox i386 1.5.0.5-0.el4.1.centos4? Thanks.