To make the search bar longer, we need to add a couple of CSS rules to a file named userChrome.css.
This file is located in your profile directory. It can be located at
c:/documents and settings/logged in username/Application Data/Mozilla/firefox/Profiles/

If it is hard to find the profile you can install the the Chrome Edit Extension from
http://downloads.mozdev.org/cdn/chromedit/chromedit.xpi

After installing the extension, restart Firefox.

Next, click on the Tools menu and choose Edit User Files.
You will be shown a new window that has five tabs on it. These tabs represent all of the user
files that you can modify to customize the Firefox browser. The first tab will be named userChrome.css
this is the file that we want to modify.

Else open it in your text editor and look for the following lines


#search-container, #searchbar {
width: 200px !important;  /* < ----- change this pixels as you like. 400px is more than enough. 200 sits quite in the layout and make readable */
}

Save the file, in ur texteditor or by clicking the Save button at the bottom of the Chrome Edit window
and restart Firefox.

Now you will notice that your search bar size is changed.

Thats it.