Running multiple versions of Opera is easy, just install to another folder. 🙂
However doing so for Firefox is a tricky. I used the following site as a reference, consider this post a mini-tutorial for achieving multiple versions on Windows. I’ve tried this with Firefox versions 1.0, 1.5 and 2.0 on Windows.
First make sure you install the Firefox versions in separate folders. To do so you will have to do a custom install so you can point them to separate folders (be sure to create a new folder before you install). Your shortcuts to Firefox in the Quick Launch, Programs folder and on your Desktop will end up being overwritten by each other; Thus, you will end up having to create a shortcut for the other versions later on.
We need to create a few profiles so we can separate our extensions and settings for each version. Create a copy of your shortcut to Firefox and lets rename it to Firefox Profile Manager. Now right click it and pick Properties. In the Target add “ -profilemanager” to the end (without the quotes and be sure to have a space before the dash), now press Apply and OK. Now make sure Firefox isn’t open at all (close all Firefox windows). Now double-click on that shortcut we made (Firefox Profile Manager) and it will open up a prompt. Here you can create a new profile and name it something that makes sense like firefox1, firefox1_5 or firefox2. This will give us a profile to tie a certain version of Firefox to. To set a profile automatically to a certain version you need to make a shortcut to the version of Firefox you want and add “ -P profilename” to the end (without the quotes and don’t forget the space before the dash).
Lets go ahead and do this:
We’ll modify the shortcut to Firefox 2 by changing its Target to something like this
X:\Program Files\Mozilla Firefox\firefox.exe -P default
And you can set your Firefox 1.5 Target to something like this:
X:\Program Files\Mozilla Firefox 1_5\firefox.exe -P firefox1_5
And you can set your Firefox 1.0 Target to something like this:
X:\Program Files\Mozilla Firefox 1\firefox.exe -P firefox1_0
Be sure to change the Start in field in the shortcut to match the folder path used in the target (however the Start In will not need the -P profilename). Also note which shortcut you are modifying (what folder it’s pointing to and what version it is, along with what profile you want it to use), it’s easy to get confused. Firefox will not remember what version the profile used last, that’s why you need to point to the proper folder. Please note, if you have Firefox open while trying to access the Profile Manager it will just open up another window of Firefox. You can’t run more than 1 version of Firefox simultaneously, so if you need to test things, you have to test everything in one version than close all your Firefox windows and then start up the other version.
One annoyance is that it will ask you whether you want the browser to be the default or not. If you change the default to another version it may ask you again when you open the other version (this is the case for both Opera and Firefox). For multiple version of IE, I normally just use an old Win98 or Win2000 box. You could also use a free virtual machine like VMware Player/Server, Microsoft Virtual PC or Bochs. There is a hack to create virtual machines in VMware Player if you dont want to use VMware Server to create them (VMware Player is lighter on resources than the Server version).