NimRecorder has been disabled in latest version of Firefox.

Document ID : KB000035836
Last Modified Date : 05/11/2018
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After the most recent update to Firefox (43.0.1), NimRecorder has been disabled in by default in Firefox.

In order to use it, you will have to manually enable it.

At the most recent update to Firefox (43.0.1), NimRecorder has been disabled in Firefox. 

I do not see an approved version available for the current version of Firefox.
e2e_appmon monitoring scripts that ran in FireFox no longer run and these web pages are no longer monitored

nimrecorder error in firefox when add-on not enabled

Recycle the firefox browser.
UIM Server:  any release 
e2e_appmon_dev:  any release
There is a way to enable the add on for Nimrecorder from about:config 

Override add-on signing (advanced users): You can temporarily override this setting by changing the xpinstall.signatures.required preference to false in the Firefox Configuration Editor (about:config page). 
Open about:config:
In the Location bar, type about:config and press Enter.
  • The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise! to continue to the about:config page.
Once you change the setting from true to false and relaunch Firefox, you will see the screen below for the nimrecorder extension.

nimrecorder add-on enabled confirmation page

Relaunch the Firefox browser.

For later releases of Firefix (starting with 5.7), the 5.2.551.1 versions of the NimRecorder is considered a legacy add-on and cannot be enabled in the Firefox browser.  You will see something similar to the following for this add-on:

NimRecorder could not be veriried for use in Firefox and has been disabled - legacy add-on disabled permanently

Access the Mozilla addons page and search for the NimRecorderNew addon at the following link:

Install this new NimRecorder add-on (version 6.0.1346) for use with your Firefox browser.
This should work for all Firefox browsers versions 57 and later.
Additional Information:
Info From Mozilla web page: 
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