User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0

Steps to reproduce:

In Firefox Quantum 68.0 (64-bit, Linux): When I am already running Firefox using a given profile: Attempt to open Firefox again with the same profile.

For example, let's say I have a Firefox instance running in a profile we'll call Profile1. I then enter the command "firefox --new-instance" and, upon being prompted to choose a user profile, I select Profile1.

Of course, I should not be doing this in the first place, because I am already running an instance using Profile1, and I cannot run two instances using the same profile simultaneously. So we're assuming that I have forgotten that I already have an instance running with Profile1 and I therefore mistakenly tried to start a new instance using Profile1.

Actual results:

There is a lag of about 5-6 seconds, then an error message saying "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."

This is the error message that typically (rightfully) appears when Firefox is not responding and a user tries to open a new instance of Firefox. However, in the case that this bug report is regarding, the error message claiming that Firefox is not responding is false because, in fact, my Firefox instance running Profile1 is still responding and functioning as normal.

Expected results:

What should have happened is exactly what happened in previous versions of Firefox: The 5-6 second lag time before the error message appears should not be present, and the text of the error message should be accurate instead of falsely claiming that Firefox is not responding.
In previous versions of Firefox, the error message said something along the lines of "The selected profile is already in use" or "Firefox is already running in the chosen profile"; I don't recall the exact wording.

Therefore, the problem in Firefox Quantum 68.0 (64-bit, Linux) is two-fold: There is now a 5-6 second lag time before the error message appears (whereas in previous versions of Firefox, the error message appeared immediately), and the error message is now inaccurate (it falsely claims that Firefox is not responding, when it should instead say that the chosen profile is already in use).

It looks like a similar bug did exist a long time ago (see bug 459638). However, since that was 11 years ago and it had already been fixed and everything was working as intended, I am submitting a new error report since the issue has just re-arisen.

To be clear, I am unsure if 68.0 is when the bug appeared, because I hadn't updated Firefox in perhaps a few months or so.

The 5 second lag is because the way we attempt to lock profiles has become standardized and we always spend 5 seconds attempting to lock in case another firefox is in the middle of shutdown.

The change in message is from bug 1533677.

I think the main issue here is that the profile locked dialog needs different wording when attempting to startup with remoting disabled.