For all of those who just downloaded Firefox 1.5 and can't get your extensions to work. This is a simple modification of Firefox's configuration to trick the extensions to work. No need to manually edit the extensions to get them to work.
- At the location bar, enter: about:config. This will show you a list of Firefox internal preferences.
- Right-click on the list, select New > String. Enter "app.extensions.version" (without quotes) for the preference name.
- Then, enter "1.0" (without quotes) as the value for app.extensions.version.
- Restart Firefox 1.5, then enable those disabled Firefox extensions.
- Restart Firefox 1.5 again to active the extensions.