Firefox: erratic starting behaviour with symlinked config file

[impert]

Hi all,

Here's a small puzzle.
As a multibooter, I keep all my stuff on a separate partition which I access via symlinks in my home directory. For instance, .mozilla --> /SDA4/guff/.mozilla. Recently I've noticed this seems to upset firefox in some distros - it sulks, and won't start. Ok, I removed the symlink, and it starts - but of course I lose all my tabs, bookmarks and preferences. Remove (rm -r) .mozilla, and copy /SDA4/guff/.mozilla to HOME, and it starts again. That shows it's the symlink, doesn't it? To prove it, I copied the .mozilla to a new folder, /SDA4/temp/.mozilla, removed the .mozilla folder from HOME, and made a link to /SDA4/temp/.mozilla. Couldn't possibly work, could it? But it did. Why?
It's not an ownership/permissions issue; I've checked.
It's totally repeatable, I've copied /SDA4/guff/.mozilla to another new folder /SDA4/test/.mozilla and linked that: firefox starts. Change the link back to /SDA4/guff/.mozilla: it won't start. I can't find any error message on this distro, ** on another I got a message about "invalid symbolic link" when trying to start ff in a terminal. **
**Oops.: No. It was evolution that gave this message:" FAILED: Invalid cross-device link" (there's a similar symlink with evolution)

Neatest correct answer gets my hearty thanks.

[stumbles]

Instead of a symlink maybe a hardlink?

[impert]

Thanks for the reply.
When I tried this, I got "hard link not allowed for directory" - which is about what I expected.
I'm a bit embarrassed because I forgot that the last time I had the problem was with evolution, not firefox. (Short term memory seems to be fading). I'll edit my last post.