Reading mail problems (Mac/PC Mozilla differences?)

I've written about my Mozilla problem in another thread ("Reading mail
from a CD-R"), but since I haven't received any replies and I've done
some further experimenting I thought I'd create a new thread.

The problem is that I'm not able to read my mail when it's stored on a
CD-R, whereas this works perfectly in Windows. I'm using the exact same
Mozilla version on both platforms, and (as far as I know) the settings
are the same as well.

I've been looking through all possible reasons for this, and one of
them is that Mozilla isn't able to write/update index files or whatever
on the CD-R, while on the Mac hard-drive it can (that still doesn't
explain why it works fine on the PC, in Mozilla!), so I tried this
little experiment:

1) In Mozilla on the Mac I created a new email account with ficticious
servers etc.

2) In a completely different location from where the Mozilla mail is
usually stored on the Mac hard-drive I created a mail folder and copied
over some of my email files/folders).

3) Editing the email account I just created I changed the existing
"Local directory" (found under "server settings" for that email
account's properties) to the new folder.

4) I quit Mozilla, then restarted it.


Yup, my email from the new folder was perfectly readable!
So I've determined that the problem isn't that Mozilla won't allow me
to read mail from anywhere other than within the profile folder
So, in theory at least, reading mail from another form of media (i.e. a
CD-R) should also work fine.

Then moving on to part 2 of my test, assuming that the problem must be
that Mozilla can't write/update index files or whatever it needs to, I
quit Mozilla again, set the newly created mail-folder to "read only",
restarted Mozilla and guess what?
I could still read all my email!!!

So, seeing that the problem is neither that my mail on the CD-R is in a
different location or can't be written to, why doesn't this work?