Redhat 8.0 is build on gcc 3.2 (as SuSE 8.1)
The Javaruntime from SUN is build on gcc 2.x. These two compilerversions produce incompatible binarycode. This leads to the problem that Mozilla (or any other browser) from the distribution cannot load the plugin for java..
You all have to wait until SUN compiles there JVM with gcc 3.2. Until this happens you may download the prebuild binary from Mozilla (but this often leads to problems with the RPM-Database). A better way is to download an unpack the prebuild Version of Phoenix
unpack it with tar x
fz to /usr/local and remove the pluginfolder with rm -r plugins.
Then make a link from your local Mozilla-Pluginfolder where the javalibrary resides (e.g. ln -d /opt/mozilla/plugins /usr/local/phoenix/plugins).
You may then start Phoenix with /usr/local/phoenix/phoenix and enjoy Java