firefox/thunderbird doesn't render accented characters

[Mike Wright]

Hi all,

Currently using f10, although I can't say for certain on which version 
this problem appeared.

Both firefox and thunderbird replace accented text with a 
black-backgrounded question mark.  If I wget these files the characters 
display correctly.  If I save them from either of the mozilla apps the 
files are saved with the replaced characters instead of the originals.
View source on firefox is useless because even the source is mangled but 
with thunderbird I can see replacements such as these: =A0, =B9, =E6. 
Just in case those get mangled they are "equal-sign capital A zero", 
"equal-sign capital B nine", "equal-sign capital E six".

I've tried setting character encoding to utf-8, utf-16, iso-8859-1, 
iso-8859-15, windows-1252 with no effect.

This is particularly horrible on the mailing lists where an email will 
display properly but when replied-to arrives mangled with black blotches 
throughout.  The longer the thread the more black appears until it 
reaches a point where it is not even worth attempting to read it anymore.

Does anybody know what this is about and what I can do to remedy the 
situation?

Thanks for any help,
Mike Wright