XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> Install Firefox 3.5 side by side with Firefox 3.0 on Windows
Install Firefox 3.5 side by side with Firefox 3.0 on Windows

Install Firefox 3.5 side by side with Firefox 3.0 on Windows

Installing Firefox 3.5 overrides your current installation by default. If you want to retain your older version, for instance because you are not convinced 3.5 is so great or because you’re a web developer, then this article explains how you can install and use 3.0 and 3.5 side by side.

Quick instruction

Most web developers or more experienced computer users do not need to be taken by the hand. Here’s a one-minute overview of how you can install and configure Firefox 3.5 without harming existing Firefox installations:

  1. Download Firefox 3.5 (other) and install to a different directory.
  2. Create shortcuts on desktop or quicklaunch by hand, one for each version.
  3. Set a profile as startup parameter for each of these shortcuts:
    1. For FF 3.0: c:\path-to-3.0\firefox.exe -p OldFF30Profile
    2. For FF 3.5: c:\path-to-3.5\firefox.exe -p NewFF35Profile
  4. Decide which one becomes your default browser. Add -no-remote flag to the non-default version:
    1. If default browser  must be FF 3.0, then change FF 3.5 shortcut:
      c:\path-to-3.5\firefox.exe -p NewFF35Profile -no-remote
    2. If default browser  must be FF 3.5, then change FF 3.0 shortcut:
      c:\path-to-3.0\firefox.exe -p OldFF30Profile -no-remote

That’s all there is to it. You can now safely browse either of them. If you want to use the same profile, you’ll need to synchronise the profiles between each other when you use them, the Firefox Add-on Profile Manager and Synchronizer can help you with that process.

Before you start all this, it is a good idea to backup your profile. You can do that with the Add-on I just mentioned, or you can do it by hand. There’s an excellent instruction of where to find your profile.

Did this instruction go to quick? Try the step-by-step instruction below:

Step-by-step instruction

TBD, sorry, may take a while before I have a clean system again to create the right screenshots…

Tip: copy original profile

You can have Firefox 3.5 start with a blank profile and it will fill-out one for you. But if you want to use the same profile you had with Firefox 3.0, yet you don’t want the original overridden, you can follow these steps:

  1. Exit all running Firefox instances
  2. Locate your profile and copy the whole directory to a new location
  3. If anything goes wrong, you can restore the profile by simply copying it back.

More info on backing up and restoring profiles can be found in this excellent article with detailed instructions from the Mozilla.org website.

As mentioned in the quick instruction you can use the excellent (but still very much in beta) Firefox Add-on Profile Manager and Synchronizer.


These instructions can be found on many places on the internet, however, I noticed they’re rather hard to find through Google, but perhap I just didn’t use the right keywords for searching. Adding a dedicated article perhaps improves the visibility of this subject and makes it easier for people to try out Firefox 3.5 alongside Firefox 3.0.

Of course, it also helps me remembering how easy it can be to install them next to each other. I tend to forget those things and it always takes a while before I find the right instructions again.


Should there be a conclusion? Not really. But I would love to see a next version of Firefox which just asks at the beginning of the installation whether I want to install it side by side and also allows me to copy (not move!) the profile, so that I can play with it without any risk. Add-on failure is a common problem when moving to a new Firefox version, which is why I’m often hesitant to completely move to the most recent version.

It could’ve been so much easier…

– Abel –

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