More icon problems (FB 0.8, OSX 2.6)

Can anyone explain this?  If I specify Firebird as "open with" on the 
Finder "GetInfo" screen, the icon does not change to one reflecting 
Firebird.  Doing the same for Mozilla or Safari does create a new Finder 
icon.  In all cases, the "GetInfo" behavior is independent of the 
default browser.

Is there an easy way to get a Firebird icon on the Finder view of an 
HTML file?  Why doesn't setting Type/Creator to TEXT/MOZB accomplish 
that? 

I can generally paste the Firebird icon into a "GetInfo" window, but 
it's really not worth the effort.  And even then, the paste is not 
always successful.  I once had 2 files with the same Type/Creator code, 
one would take the "GetInfo" paste, and one wouldn't.  I suspect the 
reason is in ancient Mac folklore.  Can anyone bring me up to date?