Here is quick steps to install Flash Player 9 plugin for firefox on Gnu/Linux. Just uncompress and run the install script, no root level permissions needed for this.
[arky@lab Desktop]$ tar zxvf install_flash_player_9_linux.tar.gz -C /tmp
[arky@lab ~]$ ls /tmp/install_flash_player_9_linux/
[arky@lab ~]$ /tmp/install_flash_player_9_linux/flashplayer-installer
Copyright(C) 2002-2006 Adobe Macromedia Software LLC. All rights reserved.
Adobe Flash Player 9 for Linux
Adobe Flash Player 9 will be installed on this machine.
You are running the Adobe Flash Player installer as a non-root user.
Adobe Flash Player 9 will be installed in your home directory.
Support is available at http://www.adobe.com/support/flashplayer/
To install Adobe Flash Player 9 now, press ENTER.
To cancel the installation at any time, press Control-C.
NOTE: Please exit any browsers you may have running.
Press ENTER to continue...
----------- Install Action Summary -----------
Adobe Flash Player 9 will be installed in the following directory:
Mozilla installation directory = /home/arky/.mozilla
Proceed with the installation? (y/n/q): y
NOTE: Please ask your administrator to remove the xpti.dat from the
components directory of the Mozilla or Netscape browser.