nightly tester tools addon, use that and you will be able to override compatability.. (this does the work of editing for you)
be warned it could cause problems (if older apps are not coded right for the new version of firefox) so make sure you have session manager that can autosave for you.
I have a seperate delicious accounts for both work and personal bookmarks. I used to use both the official Delicious extension and Delicious Complete Firefox extensions, which gave me a separate browser button for each account. Firefox 3.0.1 broke a lot of add-ons, however, including Delicious Complete, so now I can only post to one account at a time. Logging in and out all the time proving to be a hassle. I searched the Mozilla site but all of the alternatives I saw are still incompatible with 3.0.1.
I've heard there is a trick to edit the XPI, which I guess is my backup plan, but does anyone know if there is a 3.0.1-supported Delicious alternative to the official add-on?