But before we begin, please note that this tutorial will work only on Firefox 3.5. It will not work on later versions like 3.5.1 or 3.5.2. So it is needless to say, if you want to proceed further with the tutorial and you have version 3.5.1 or 3.5.2 then you need to downgrade to 3.5. Uninstall the earlier version first, restart your PC and then install Firefox 3.5. Once you are ready, proceed with the following steps.

1) Download the Strata4.0 theme here (created by SpewBoy. All thanks.) but don’t install it as of now. Just extract its contents into a folder and then launch Firefox 3.5.

2) Now, in the Firefox 4.0 screenshots depicted by Mozilla, the ‘Stop’ button is at the end of the address bar. So we will too place the ‘Stop’ button at the end of the address bar. For this, right-click just below the address bar and a menu will be displayed. Click ‘Customize’ and a window will appear. We are least concerned with this window. Just drag the ‘Stop’ button to the end of the address bar and close that window.

3) Now open the ‘Add-ons’ window (Tools >> Add-ons) and drag-n-drop the ‘strata40_v02.jar’ file from the extracted folder on it. Install the theme and restart Firefox.

4) Now download an add-on called Personal Menu. Install it and you will have three new toolbar buttons next to the Stop/Reload button. Now if you are on Windows XP then skip step 5.

5) This step should be followed by Windows Vista/Windows 7 users only. Download and install an add-on called All Glass Firefox Mod. This will give a superb glassy look to Firefox.

6) Now we need another add-on called Stylish. Install it and you will see a very small ‘S’ icon at the right most end of the status bar below. Right-click it and select ‘Write new style >> Blank style…’. In the window that appears, enter name as ‘Strata Glass Fixes’ and in the big textbox below, copy and paste all the contents of the ‘glasser fixes.txt’ file from the folder extracted earlier. This will fix the display of tabs. Now the tabs will become crisp and clear.

7) Almost there! Now we will customize the download bar according to the one showed in the Firefox 4.0 screenshots. It will be just a green line below the address bar which looks really really awesome and aesthetic. So, take a deep breath, have some water and download an add-on called Fission and install it. Now go to its options and browse for the ‘loading_progress.png’ image file in the extracted folder. This addon basically changes the download bar and shows an image that is selected in its place.

The final step. Now we will merge the address bar and search bar into one just as showed in the Firefox 4.0 screenshots (also like in Chrome). For this, download the Omnibar add-on, install it and restart Firefox. If you followed everything right, this is what you can expect:

Enjoy Firefox 4.0 look-n-feel. All the credit goes to the respective add-on creators.