How to run firefox and firefox ESR simultaneously

The main reason I want to use firefox ESR is to use a proprietary database tool for work that only allows oracle-java based web logins for linux (or a windows only thin client). I also want to use the full version of the outlook web application which only works in firefox. I don't want to run the NPAPI plugins for normal web browsing and email.

I have the repo version of firefox installed and firefox ESR installed in /opt/firefox and linked to /usr/local/firefox-esr

When I run firefox any attempt to run firefox-esr either brings up a window without the NPAPI plugins.

If I try running with the --new-instance or --no-remote options I receive the following error:

Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system.

Regardless which one I start first, I can only open that one, and get the above error if I attempt to sidestep.

What makes this an especially annoying problem is that I often have to respond to emails that I need to access the database to deal with. So either I close and open many windows.

You need to use -no-remote option, as in firefox -no-remote.

From man firefox:

-no-remote

Don't connect to any other running instances of firefox. Use this if you want to run firefox in an entirely new process. By default, firefox will delegate a command to an already running instance.

You'll also need separate profiles for Firefox and Firefox-esr, which can be created with with firefox -P Profile Manager.