Hi Naomi

>This https://addons.mozilla.org/en-US/firefox/addon/1419 gives me an error when I tried to install it.

It is pure FF3 extension so if you are adventurous then install FF3 and use the extension. There is an extension called MR Tech's Local Install which allows FF2 subversion incompatible extensions with higher FF2 version but I am not sure it will be useful for FF3 downwards to FF2

Hope it helps.