hmm.. i dont know, really.
only thing id suggest to do is try and update firefox to the latest version. youll need to use your package manager to do this.
check out this
link to read about your package manager in FC (called yum). after reading how it works, try and update firefox to the latest version that is supported/listed with yum.
edit: i just noticed that on the site it says that the document is for FC4.. and your using FC3. it also has a link which describes how to get it to work with FC3.. id say just try it how the FC4 document says, and if it doesnt work then do the extra step.