There are two ways i have managed to run multiple instances of FireFox browser on macOS. One is slightly technically involved and another one is straight forward.
The straight forward method of running multiple versions of firefox is to download different versions of firefox and installing them/renaming them as needed. For example Firefox offers following versions
- Select any versions of interest (Firefox, Firefox Extended Support Release, Firefox Developer Edition, Firefox Beta, Firefox Nightly edition etc) from this url https://www.mozilla.org/en-US/firefox/all/#product-desktop-release
- Upon installation if you are prompted that Firefox application already exists, chose to keep both and then rename the application to a unique name within the /Applications folder.
The technically inclined method is to create different profiles for a single Firefox instance using Firefox Profile Manager (inbuilt within the browser) and use Automator script to launch the specific profiles.
- Use the Profile Manager to create multiple profiles as described in this help page https://support.mozilla.org/en-US/k...-remove-firefox-profiles&redirectlocale=en-US
- Use Automator to create a new Application (File -> New -> Application). Select "Run Shell Script" as the action and enter the command "open -n -a Firefox --args -P <profile-name>" where the <profile-name> must be replaced with your specified profile name on step 1.
- Save the Automator script somewhere in the computer like Documents folder. If needed you can chose to add a Firefox icon to this application by selecting the "Get Info" option on the right click menu of the saved Automator application and drag an .ico file of. your choice from the web into the icon location.
- Double click the saved Automator script application to launch a new instance of the Firefox browser and right click on the dock to select options -> keep in dock, if preferred to keep the application on the dock.
There are few drawback in having multiple profiles of a single Firefox application running as i have described in the second method.
- When one instance of a Firefox crashes or freezes, all the running instances will end.
- All Firefox instances share the same application memory pool. This may be a security risk in certain use cases.
- Backup and restore of the profile settings, Automator application become important in this use case if a new version removes the custom profiles or there is a need to reinstall them.
- Updating of Firefox cannot happen until all running instances of Firefox browsers are closed. Can become annoying quickly.
After trying the second method for a long time, i have resorted to the first method and use a plugin called "Firefox Multi-Account Containers" within the browser to keep separate work-spaces for individual websites/web applications. This can be accessed here
https://addons.mozilla.org/en-US/firefox/addon/multi-account-containers/
Hope this helps. If you have any questions, let me know.