by 
Few days ago I have finally decided to give a try to Debian 7 on VirtualBox after I downloaded it long time ago. After installation procedure I faced with few issues which I could managed to solve them with a bit searching and work. Here I summarized the issues with the solutions.
Installing graphic driver
The first important issue which is quite popular on VirtualBox is installing graphic driver. If your do not install the driver Debian will not be able to run GNOME 3 and just could run GNOME classic inefficiency. If you are not sure about installation of the driver, easily try to resize your Guest OS screen, if it was successful means it is installed, otherwise you should install it.
For installing the driver you need to download Guest Additions (GA) on your host computer (assume Ubuntu, Windows, etc.). The GA package is an ISO file. After downloading it, you should mount it but keep in your mind that before installing GA, you have to install its dependencies to avoid facing with errors and further issues. For installing the dependencies type the following commands on Debian terminal (keep in your mind that you should have root user access).
# apt-get install build-essential module-assistant
# m-a prepare
The first line install all necessary packages which needed by GA and in the second line module-assistant grab the needed headers. In the next step you need to reboot Debian and then install GA.
Note: Bear in your mind that after installing GA, you need to enable 3D mode from VirtualBox –> Settings –> Display –> tick “Enable 3D acceleration”, in order GNOME 3 runs efficiently and smoothly.
Installing Firefox
Debian 7 (overall versions after 2006) delivered with Iceweasel browser which is a free software re-branding of the Mozilla Firefox browser distributed by the GNU project. Overall it is good browser but sometimes you may face with compatibility issues on the website or when you want to install Firefox add-ons or plugins. Therefore, you might want to replace it with original Firefox. For installing Firefox you need firstly to remove current Iceweasel with below command,
# apt-get remove iceweasel
Then you should add Linux Mint repository to Debain with editing the file in “etc/apt/source.list” and below line to the file,
deb http://packages.linuxmint.com debian import
Then update your package list
# apt-get update
Running above command returns you error because valid GPG key is not provided, so you should add GPG key with following commands.
# gpg --keyserver pgp.mit.edu --recv-keys 3EE67F3D0FF405B2
# gpg --export 3EE67F3D0FF405B2 > 3EE67F3D0FF405B2.gpg
# apt-key add ./3EE67F3D0FF405B2.gpg
# rm ./3EE67F3D0FF405B2.gpg
Finally, install Firefox browser with this command,
# apt-get install firefox firefox-l10n-en-us
Installing non-free flash player
Debian delivered with Free version of flash player which is buggy and has high RAM and CPU consumption in comparison with non-free flash player which increase more system load. You easily can install the non-free version with running the following command in terminal.
# apt-get install flashplugin-nonfree
In order to make sure that the plugin installed successfully, open your Firefox plugins tab (Your browser plugins tab) you should see Shockwave Flash xx.xx plugin.
