I also have a few questions:
1) Which version of Firefox do you use? you can check by going to the Help>About area, and telling me your version number.
2) Which extentions do you have installed? Please list all of them as well as their version number.
3) What kind of computer do you have? How's the RAM, and how's the processor?
4) Do you keep your system spyware-free?
Finally, the quicktime link seems like you've got your MIME settings fucked up in Quicktime itself, though I'm not positive. You can check the settings by opening the Quicktime icon in your Windows Control Panel, and doing the following:
>click the Browser tab
>click the MIME Settings box
>Check and see if the MP3 box is checked. If it is, uncheck it. If it isn't check it. See if that helps.
>Check to see if the sub-setting for WAVE in the Audio - Audio only file formats area is checked. If it is, uncheck it. If it isn't, check it.
Hopefully this stuff helps.