Recently, notification popped up in my browser and said that my flash player was outdated and I should update it. If this happen to you, you can find instructions below.
Go to Adobe Flash player download page:
Download .tar.gz package.
Extract archive in graphical environment or open Terminal, navigate to download directory and type:
tar -xvzf install_flash_player_11_linux.x86_64.tar.gz
Go to Iceweasel directory:
Copy file libflashplayer.so to plugins folder:
cp /<download_directory>/libflashplayer.so ./
mv /<download_directory>/libflashplayer.so ./
This will move file instead of copying it.
Thats it! Your Flash Player is now installed, you can see it under Menu>Add-ons>Plugins in Iceweasel.