Sfdwhf

Searching on Google I found the answer.

xdg-open opens a file or URL in the user's preferred application. If a
URL is provided the URL will be opened
in the user's preferred web browser.
If a file is provided the file will be
opened in the preferred application
for files of that type. xdg-open
supports file, ftp, http and https
URLs.

xdg-open is part of xdg-utils package and it's already installed on Ubuntu 10.10.

You can also use:

x-www-browser http://some-url.org

And it will open the URL in the default browser.

With default Ubuntu setup only gnome-open command comes to mind.

gnome-open http://askubuntu.com

I played around this a little.
There is a problem with gnome-open — it won't invoke the default web browser unless you specify a url.
That's a problem if you want to set up an icon or a shortcut that will always launch the browser that is set as default.
Other times you might need to set it as a parameter for some programs that require a link to a web browser and don't work well with gnome-open (e.g.: acroread).
You might solve this by using either x-www-browser or gnome-www-browser system links that you can set up through update-alternatives, but those are system wide settings, not user specific (and they are not synchronized with the values set through gnome-default-applications-properties.
All this can be solved by opening the sensible-browserexecutable (which is actually a script):

sudo gedit $(which sensible-browser)

and adding this at the beginning:

#!/bin/bash

BROWSER=$(gconftool -g /desktop/gnome/url-handlers/http/command)

export BROWSER="${BROWSER//""%s""/}"

That will make sensible-browser always launch the user-specified default web browser.
(I found out that gnome-default-applications-properties changes some gconf keys according to the browser that is currently set. The default browser value can be obtained from any of these keys so I went for /desktop/gnome/url-handlers/http/command and used it to fill the $BROWSER variable (the value is stripped of the "%s" part). )

Just that you may find it useful. A fallback approach, and one liner.

URL="www.url.com/some"; xdg-open $URL || sensible-browser $URL || x-www-browser $URL || gnome-open $URL

Good reading for the no familiar with the logical operators
https://www.howtogeek.com/269509/how-to-run-two-or-more-terminal-commands-at-once-in-linux/.

Follow below commands :

1. 
   $ type -a Firefox : This gives path to firefox application


2. 
   $ /usr/bin/firefox www.facebook.com : This opens a tab with www.facebook.com