Published at LXer:

In this tutorial we will see how to install Adobe Flash in Debian Etch/Lenny/Sid. Adobe Flash (previously called "Macromedia Flash"') is a multimedia platform created by Macromedia and currently developed and distributed by Adobe Systems. Since its introduction in 1996, Flash has become a popular method for adding animation and interactivity to web pages; Flash is commonly used to create animation, advertisements, and various web page components, to integrate video into web pages, and more recently, to develop rich Internet applications.

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If all else fails, download install_flash_player_10_linux.tar.gz from Adobe, decompress, cd to resulting directory, then run as root:
./flashplayer-installer
Tell it to install in /usr/lib/iceweasel (and/or where ever else you want).
Works for me.