Using firefox 3 and 4 on the same machine

Well, I am tester and need to test the page layouts in many browsers including multiple versions of the same browsers. MS doesn’t support having two versions of IE on the same machine (so dumb!) but dear Firefox does. When I googled how to have Firefox 3 and 4 installed on same machine side by side all the articles that came up referred to FF3.16 and FF4 beta. However FF4 is officially out for some time now but none of the articles talk about it. So here is how to do it.

Install Firefoxes

1. Download FF3 & FF4 
2. Install FF3 first. While installing change the default folder where FF is installed. I changed it to
   C:\Program Files (x86)\Mozilla Firefox\v3.6.16 
3. After the installation is complete, rename the shortcut from ‘Firefox’ to ‘Firefox3’ 
4. Install FF4. Again, change the default installation folder. I changed it to
   C:\Program Files (x86)\Mozilla Firefox\v4.0 
5. Rename the shortcut to ‘Firefox4’

Now you have both the versions on the machine however they both share the profile, which means that your settings, preferences and other user items will be shared between the two versions. If that is what you want then you are all set.

Create Profiles

In case you don’t want the two versions sharing all those settings then you will have to create separate profiles for each of the version.  Follow the rest of the steps to do so:

1. Open the profile manager:
Start --> Run; enter following text in the run box and hit enter “C:\Program Files (x86)\Mozilla Firefox\v4.0\firefox.exe” -ProfileManager  (NOTE: Using the path for FF3 will open the same window)
2. The Profile Manager will open with the single profile “default” which is shared by both versions, so go ahead and delete it.
   
   
3. Now click ‘Create Profile’ and hit next on the first step
   
4. Enter a name for the profile ‘FF3’ and click ‘Finish’
5. Repeat step 3 & 4 to create profile ‘FF4’
   
6. Close the profile manager by clicking ‘Exit’

Link profiles to versions

You have the profiles setup and the only thing remaining is to link each one of them to their respective executable. So follow these remaining steps to complete the whole process:

1. Right click on the FF3 shortcut (created in Install Firefoxes - step 3) and click ‘Properties’
2. Add the text “-p FF3” at the end in ‘Target’ field (so that it looks like below). Click OK
   
3. Repeat steps 1 & 2 for Firefox 4 shortcut to use FF4 profile

That’s it!

Catch: You cannot run both the Firefox versions at the same time though, either FF3 or FF4 at a time. If you are using FF3 and want to switch to FF4, you will have to close all instances of FF3 and then open FF4 or vice-versa.
Let me know if there is any way you can run both at the same time.

Note: I am using Windows 7, so you will have to do any OS specific changes if you are using any other OS.

Credits:

1. My boss Ken
2. http://www.thewindowsclub.com/how-to-run-firefox-3-and-firefox-4-simultaneously-in-windows