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I've a laptop on which Windows 10 Home Single Language 64-bit Operating System is installed.

I've installed the web browser 'Firefox Quantum 63.0 (64-bit)' on this laptop.

Then, I installed the web browser 'Firefox Developer Edition 64.0b4 (64-bit)' on this laptop.

I downloaded the 'Firefox Developer Edition 64.0b4 (64-bit)' installer file from the web browser 'Firefox Quantum 63.0 (64-bit)' and started the installation process by clicking on the downloaded installer file.

During the installation process only a dialog box appear having the below message :

Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window.

Then I closed the web browser 'Firefox Quantum 63.0 (64-bit)' and then the installation of web browser 'Firefox Developer Edition 64.0b4 (64-bit)' got done.

Also, when I open one of the both browsers and then try to another browser the dialog box with the same message appear, I've to close the opened browser and then the other browser can be opened.

Few days ago, this was not the problem on my laptop. I was able to use both the Firefox browsers at the same time on my laptop. But, I don't know why and how this problem suddenly started.

For your reference below is the screenshot of the dialog box that appears

Locations of the .exe files at which both of these browsers are installed are as below :

  • 'Firefox Quantum 63.0 (64-bit)' : "C:\Program Files\Mozilla Firefox\firefox.exe"

  • 'Firefox Developer Edition 64.0b4 (64-bit)' : "C:\Program Files\Firefox Developer Edition\firefox.exe"

marked as duplicate by Ramhound, Run5k, fixer1234, PeterH, music2myear Nov 1 '18 at 17:56

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • So what is your question? Is each instance configured to run separate profiles and are installed to different directories? Please edit your question and include this vital information – Ramhound Oct 28 '18 at 7:01
  • @Ramhound : Please check the installation locations of both the browsers on my machine. I've appended the details to the question body. I don't understand what does it mean by configuring the browser to run separate profiles. Thank You. – JSLover Oct 28 '18 at 7:18
  • What exactly don’t you understand? Verify if you have more then one Firefox profile. If you only have one, configure the second installation, to use a different profile. – Ramhound Oct 28 '18 at 7:47
  • @Ramhound : I don't understand exactly what does it mean by the term 'Firefox profile' and how to check which browser is using which profile. If both the Firefox browsers are using the same profile then I want the way to assign different profiles to each of the browsers. That would be the ultimate answer to my question. Thank You. – JSLover Oct 28 '18 at 7:49
  • 1
    Additional required reading: developer.mozilla.org/en-US/docs/Mozilla/Firefox/… – Ramhound Oct 28 '18 at 8:22

If you want to run two different versions of Firefox there's a way. First install the latest version you want to use as normal. Then download the version you want to run alongside but don't install it. Install 7zip https://www.7-zip.org/ Right click on the installer file > 7-zip > open archive. Extract the folder named core to any place you want. After extraction rename the folder if you want and create a shortcut for firefox.exe on Desktop. Now it should work alongside. You can extend this idea for multiple versions of firefox if it works. Hope that helps.

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