Hi,
Recently I upgraded my Firefox ESR to v52.2.1 and notice I can't run more Firefox instances despite the fact i have FirefoxPortable.ini set like this:
---
[FirefoxPortable]
AllowMultipleInstances=true
---
Firefox itself presented the error Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window
Did some testing and found that this version only accepts multiple instances if the -no-remote option is not passed to firefox.exe by the portable launcher.
Just to let the developers know about this...
Multiple instances means the ability to run two different versions of Firefox at the same time. Like running ESR and Stable alongside each other. Firefox doesn't normally allow this. Running multiple windows of the same version of Firefox is different. Enabling multiple instances disables the ability for Firefox to start a new window by running it again as well as the ability to pass in associated links/html files.
Sometimes, the impossible can become possible, if you're awesome!