How to make an extension or theme which was originally made for Firefox 1.5 compatible with Firefox 2.0?

First download this file : http://www12.asphost4free.com/bakuryu/extension/nightly.xpi.txt
(right click on link and click Save Link As)

then remove the .txt extension from the file.

Now start Firefox -> Tools -> Addons, and drag the nightly.xpi file onto it. Install that extension. Restart Firefox.

Now Tools -> Nightly Tester Tools -> Install Extension or Theme
browse and select your extensions or themes you want to install.
OR
If you have already installed the extensions, then Tools->Addons and click the Make All Compatible button. Now restart firefox, and the extensions will be usable.