This knowledge base article should help Installing a previous version of firefox

Note that previous versions will only be supported for a limited time. You should consider asking Yahoo and Zynga to release updates for those toolbars to make them compatible. If enough people ask, they will update the software.

thank u grease money; however, if Firefox makes an upgrade then it seems reasonable & prudent that it is Firefox's initial responsibility to create compatible software with yahoo & zynga.