Because Fast Dial 1.x replaces about:blank pages with its page, when using the Web Developer add-on (which also does this on occasion), you will run into conflicts.

This was finally resolved in Fast Dial Version 2.x.
Fast Dial Version 2.x can be downloaded here

Remember FD v2.x works only in FireFox 3.
Upgrading to FD v2.x is the Recommended solution, although there is a workaround for v1.x available: here