I am not using Windows at the moment. Are you able to check the file properties I am not sure but does that identifiey the version, at least indirectly. The User Agent String will identify the Firefox version if it is in use. (Mine for instance in ESR:
Mozilla/5.0 (X11; Linux x86_64; rv:10.0.5) Gecko/20100101 Firefox/10.0.5 )

You mention standard vs ESR, but users on standard releases should now be on Firefox 13, soon to be Firefox 14.

Maybe if you explain the task you are attempting someone will have ideas. You could also try asking on other forums such as Mozillazine.

All current ESR versions have a user agent of 10.0.x with x greater or equal to 3 (the last 10.0.x release was 10.0.2).
So 10.0.3, 10.0.4 and 10.0.5 are the ESR versions that have been released up to now.
Each new Firefox release will increase that minor version number by one until Firefox 17 gets released.

You could parse the application.ini file in the Firefox program folder (C:\Program Files\Mozilla Firefox\)

• Version=10.0.5
• SourceRepository=http://hg.mozilla.org/releases/mozilla-esr10

You can do a quick check in the About Firefox dialog box. It tells what the release channel is. If it says ESR, then you have an ESR version.

That information in Help > About comes from the \defaults\pref\channel-prefs.js in the Firefox program folder (C:\Program Files\Mozilla Firefox\)