The easiest way to instal flash and other multimedia codecs would be to use the exnoodles script in my signature. Take a look at my blog on it> http://www.linuxquestions.org/blog/c...-mplayer-2092/
If you do not want to use that you need to either use the debian-multimedia.org repo or backports.org to install flash.
Using dmm it would be apt-get install flashplayer-mozilla
Using backports it would be apt-get install flashplugin-nonfree.
Firefox is Iceweasel in debian. If you want the mozilla version take a look at> DeviceGuru » Adding REAL Firefox to Debian Lenny - http://www.deviceguru.com/adding-rea...-debian-lenny/
As for other codecs, for sun's java you need contrib non-free in your sources.list. Totem and the gstreamer plugins, mplayer with ffmpeg and w32codecs along with mplayerplug-in or vlc will give you pretty much everything else.
I assume you pretty much want to be able to play everything in your browser as well as things like dvds.
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1) Gecko/20090707 Firefox/3.5.1 (Debian-3.5.1-1)
- Adobe Reader 9.1
- DivX Browser Plug-In
- Helix DNA Plugin: RealPlayer G2 Plug-In Compatible
- Java(TM) Plug-in 1.6.0_14
- Java(TM) Plug-in 1.6.0_14-b08
- mplayerplug-in is now gecko-mediaplayer 0.9.6
- OpenOffice.org Plug-in
- QuickTime Plug-in 7.4.5
- RealPlayer 9
- Shockwave Flash
- Windows Media Player Plug-in
If you arent sure what you need in your sources.list take a look at the link in my signature.