How to make FF Portable a default - at ALL times

I am running under Win XP Pro Sp3

I used to have Firefox installed. Then I migrated to Firefox portable, by transferring the profile across. I have since uninstalled the original and deleted all associated folders.

When I click on my desktop icon, I get my portable FF poping up no problem -- with all my extensions, bookmarks and plugins.
(The icon points to C:\FirefoxPortable\FirefoxPortable.exe)

When I click on a link within Thunderbird (email client), a 'virgin' version of FF pops up. No extensions, no bookmarks, etc.
(C:\FirefoxPortable\App\Firefox\firefox.exe)

I have tried many ways to set (and re-set) my portable as default - to no avail. Why do links in TB point to firefox.exe and not firefoxportable.exe? More importantly, how do I make my full version pop up every time I click on a URL.

Baffled.

PS When the FF portable is already open, every link opens up in the correct version.