I look after a couple of web sites, and occasionaly add mp3 audio tracks.
IE works fine, Opera works fine but Firefox tells me I need add ons, which it can't find. Although I search for addons manualy, and install them, firefox still can't find them. Why can't Firefox just have these as part of the package, as the other browsers do?

post a url to test
most embedded sound files should play without plugins in firefox
I found a site that played mp3 fine
I have flash and shock plugins
I use quicktime alt never added as plugin works fine
check version of firefox I use 2.0.0.4
so user can set it up they way they want
and it's free the one's you mention have a cost
mp3's and other embedded stuff can carry spyware
even bad script can lock up a browser
by far as for me the best browser is firefox

The most current version of Firefox is v2.0.0.11. Two current security updates have been made between v2.0.0.8-2.0.0.11. It's important that you get them. There have been a few problems noted with the last 2 updates.

If Firefox requires a plug-in that is not currently on the machine, you will usually see a message to the effect that ;"irefox has prevented an option from starting up to protect your system;". There should be a "Options" button to the right of the message, where you can click to allow, within any of the three choices. Doing that should allow the plug-in to function