AFAIK, OpenOffice 2 comes as a set of RPM packages. You should be able to extract the tarball that you downloaded, change into the directory that is created, and run:
Then change into the desktop-integration subdirectory, and run the same command.
You can install Firefox using the binary that you downloaded from mozilla.com. This WILL NOT break the yum, however the rpm database will not know that it is installed. You will be able to use Firefox if you extract it to /usr/local, and make a symbollic link in /usr/bin to /usr/local/firefox/firefox.
I hope this helps, and post back if you have any more questions