Firefox U3 and Spellbound...

Is anybody aware of a workaround for installing the Spellbound extension for Firefox?

If you try from Spellbound's homepage, or by saving the spellbound_0.7.3.xpi file (right-click, "save link as..."):

It attempts to install as any other extension (opens up the software installation dialogue box, you press "Install Now", and the Extensions box pops up, displaying the progress). Problem is, it then displays the following error message(s):

"Spellbound 0.7.3/Mozilla SpellCheck Libraries 1.0.1.0 could not be installed because it is not compatible with Firefox 1.5.0.7. (Spellbound 0.7.3/Mozilla SpellCheck Libraries 1.0.1.0 will only work with Firefox versions from 0.9 to 1.0+)"

This is rather confusing because this (0.7.3) is the version it recommends when you visit the install page ["From your user agent it appears that you are using a Firefox 1.0+ Trunk build for Windows
User Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.0.7) Gecko/20060909 Firefox/1.5.0.7)].

It then takes you to a page that says:

"SpellBound version 0.7.3: Successful
Spell Check Libraries for Windows: Successful

Please restart your browser."

...which is obviously incorrect.

1) I copied the entire "spellbound@exchangecode" folder from the "C:\Documents and Settings\Administrator\Application Data\Mozilla\Firefox\Profiles\xxxxxxnn.default\extensions" folder, and pasted it in the "X:\System\Apps\3C9F7B3F-D55C-42cd-8537-B878518B73AF\Data\profile\extensions" folder, and

2) Copied the "dictionaries" folder from the "C:\Program Files\Mozilla Firefox" folder, and pasted it in the "X:\System\Apps\3C9F7B3F-D55C-42cd-8537-B878518B73AF\Exec\firefox" folder.

PLEASE HELP!!