Choose 'Solaris' from the drop-down list.
Choose x86 from the second box unless you have a Sparc system. Click on 'Agree and install now' and then 'save file'. Here I saved the file on my 'Desktop'.
What you just downloaded is a zipped folder with .bz2 extension. You need to right click on the zipped file and then choose 'Extract Here'. Now your files are extracted into a folder with the same name on your desktop. There are two files in that folder and we are interested in 'libflashplayer.so'.
Then go on the Terminal. login as super-user: type SU and then enter your root password if there is any. In this stage you have to copy the file (libflashplayer.so) into the plugins folder of your Firefox.
/export/home/tiger/Desktop/flash_player_solaris _r151_x86/libflashplayer.so /usr/lib/firefox/plugins/
Opera is also available for OpenSolaris.