Softwares available in debian
 

Can I install all softwares to debian which I was having in ubuntu?
Like firefox,chrome,vlc,and other free softwares

yes, especially seeing as those are just about THE most common packages imaginable...

Iceweasel=Firefox , that said if you want the actually Firefox you will need to download it from Mozilla. Same goes for Icedove=Thunderbird.

$ apt-cache policy iceweasel
iceweasel:
Installed: 10.0.2-1
Candidate: 10.0.2-1
Version table:
11.0~b5-1 0
1 http://ftp.us.debian.org/debian/ experimental/main i386 Packages
*** 10.0.2-1 0
500 http://ftp.us.debian.org/debian/ unstable/main i386 Packages
100 /var/lib/dpkg/status


Debian repos have Chromium, for Chrome you will need to download it from Google.

Other than that yes most packages in *buntu are also in the Debian repos.

Mozilla/5.0 (X11; Linux i686; rv:10.0.2) Gecko/20100101 Firefox/10.0.2

$ apt-cache policy vlc
vlc:
Installed: 1:2.0.0-0.1
Candidate: 1:2.0.0-0.1
Version table:
*** 1:2.0.0-0.1 0
500 http://www.debian-multimedia.org/ unstable/main i386 Packages
500 http://debian.dc-uoit.net/debian-multimedia/ unstable/main i386 Packages
100 /var/lib/dpkg/status
2.0.0-6 0
500 http://ftp.us.debian.org/debian/ unstable/main i386 Packages

$ apt-cache policy google-chrome-stable
google-chrome-stable:
Installed: 17.0.963.65-r124586
Candidate: 17.0.963.65-r124586
Version table:
*** 17.0.963.65-r124586 0
500 http://dl.google.com/linux/chrome/deb/ stable/main i386 Packages
100 /var/lib/dpkg/status

$ apt-cache policy chromium
chromium:
Installed: (none)
Candidate: 17.0.963.56~r121963-1
Version table:
17.0.963.56~r121963-1 0
500 http://ftp.us.debian.org/debian/ unstable/main i386 Packages


$ apt-cache policy google-chrome-beta
google-chrome-beta:
Installed: (none)
Candidate: 18.0.1025.45-r124098
Version table:
18.0.1025.45-r124098 0
500 http://dl.google.com/linux/chrome/deb/ stable/main i386 Packages

$ apt-cache policy google-chrome-unstable
google-chrome-unstable:
Installed: (none)
Candidate: 19.0.1055.1-r123982
Version table:
19.0.1055.1-r123982 0
500 http://dl.google.com/linux/chrome/deb/ stable/main i386 Packages

Most of the packages available in the Ubuntu repos originate in the Debian repos and are modified and put in the Ubuntu repos by the Ubuntu devs.

A very few come from the upstream source like Firefox and Thundbird.

Why bother having to create a .deb from scratch when you can get one direct from Debian and just modify the install script?

You will find anything you need in the Debian repos.

As some smart a$$ has in his sig;
Debian - "If you can't apt-get something, it isn't useful or doesn't exist"

This is true.