Daily Gyan have recently release two tips on how you can install firefox 2 extensions in firefox 3 even if they are not yet compatible with it. I have tried many of firefox 2 extensions and believe me majority of them do work with firefox 3. Including the tips by Daily Gyan here are few my tips that will let you use and enjoy your favourite extensions.
1) Use Nightly Tester Tools extension and install it. Thats all you are done. This extension will give you warning message while installing but will let you install extension.
Another problem while istalling through Nightly Tester Tool is that you can not see install button on Firefox Addon site as it is not compatible yet. And with tip from Daily Gyan you can easily see that Download button.

- Take Firefox. Type about:config into the address bar and hit enter.
- Click on “I’ll be careful, I promise!” button.
- Right click and select New -> String.
- Enter the preference name as
general.useragent.overrideand the value asFirefox/2.0.0.14

Now go to firefox extension website and enjoy power of your favourite extensions.
Tags: firefox-hacks