Running Multiple Versions of Firefox Simultaneously

(Based on information from this entry at the Dojo Foundation BLOG. This information is for Windows machines, specifically for concurrently running Firefox 1.0.7 and 1.5.0.x, but the same information applies to other versions of Ff as well. David Schontzler’s aforementioned post covers ‘Nix machines.)

As a Web developer on some fairly complex projects, it’s important to be able to run the current Firefox browser, as well as the previous release.

These instructions are based on having first installed Firefox 1.0.7.

Locate your current Firefox profile. Normally it will be in a folder under your Application Data folder, typically such as the following:

C:Documents and Settings{user_id}Application DataMozillaFirefox

Copy the entire Firefox directory someplace convenient, so you have a backup, for when you miss a step and something goes horribly wrong. (I know—this would never happen to me, either, but I was grateful I had a backup the two times I munged this setup and had to fix my initial Ff 1.0.7 installation.) You want to be able to fix your Firefox extensions in the event your running of Firefox 1.5 tries to upgrade them, which is a one-way process.

Then download and install Firefox 1.5.0.x, to a location other than the default location. (I recommend using a directory named C:Program FilesMozilla Firefox 1.5, as C:Program FilesMozilla Firefox is the default.) Do not launch Firefox 1.5 yet. (Be sure not to tell the install wizard to launch Firefox at the end.) If you do, you’ll need to quit the browser, and replace the now-upgraded profile folder with the one you backed up.

To allow you to clearly identify separate processes in the Task Manager process list, and to avoid accidentally running the Firefox 1.5 installation without the batch file that will preserve the Firefox 1.0.7 profile information, I recommend renaming the C:Program FilesMozilla Firefox 1.5firefox.exe to firefox15.exe. However, if you choose to perform this step, you’ll need to rename firefox.exe to firefox15.exe each time you perform an upgrade (such as from to of Firefox 1.5. (See “Future Upgrades,” below.)

Next, you’ll need to create a batch file to launch Firefox 1.5 and load a Firefox 1.5-specific profile:


start "Firefox" "C:Program FilesMozilla Firefox
1.5firefox15.exe" -P "Firefox 1.5"


The above batch file presumes that Firefox 1.5 is installed in the directory specified, that the executable is named firefox15.exe, and that a user profile named Firefox 1.5 will normally be used. If you’ve used values for any of these items that are different than the recommendations above, alter the portions marked in red accordingly.

The first time you launch Firefox 1.5, the Profile Manager will appear. Create a profile that matches the name used in your batch file.

If you want to change the icon shown (on the taskbar and the Firefox title bar), create a new icon and place it in C:Program FilesMozilla Firefox 1.5chromeiconsdefault with the name main-window.ico. You can find one that has a “1.5” overlaid atop the regular Firefox icon here. You can also find utilities to change the text in the title bar itself, such as the Titlebar Tweaks Firefox extension—which, ironically, has not yet been officially updated for Ff 1.5.0.x (as of June 7, 2006). You can install an updated, but unofficial, version from here.

I have also found that using significantly different themes (skins) for my different Firefox versions helps keep them straight at a glance.

And, of course, if you prefer to make Firefox 1.5 your default Ff version, do so, and modify the batch file to point to 1.0.7 instead.

Future Upgrades

The best thing to do when one is about to upgrade Firefox 1.5.x, is rename the firefox15.exe back to firefox.exe, run the ugprade, and then rename it back. If you don’t, you’ll find that your firefox15.exe is still around, but that the upgrader has added its own firefox.exe, requiring a delete-and-rename, as well as producing some interesting quirks, like Firefox not realizing it’s been upgraded because the .exe you’re running is the old one, while everything else is new.

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