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Even after closing the Fiddler application, the instance of the process is still running

Even after closing the Fiddler application, the instance of the process is still running and when I try to start Fiddler a second time, it shows prompt telling Fiddler is already running and do you want to start fiddler any way. 

If we choose Yes, then it will give another prompt telling port is in use and shall use random port.


This issue is coming only after upgrading the Fiddler to the latest version from the site 4.6.3. Older versions were fine.

  • Guest
  • Dec 9 2016
  • Will not implement
  • Attach files
  • Eric Lawrence commented
    December 09, 2016 16:13

    I've seen this happen once in a while too. Do you have any extensions installed?

  • Guest commented
    December 14, 2016 09:51

    No extensions installed. Just did an installation of the latest over the existing installation of older version.

  • Eric Lawrence commented
    December 24, 2016 19:30

    How long does the problem persist? Do you have the option to "Remove certificates on exit" enabled if you click the Tools > Fiddler Options > HTTPS > Certificate generator configuration link?

  • oli fozzy commented
    February 02, 2017 13:24

    Same problem here.

    I already try with a clean un-install, and reinstall . 


  • harri kylliainen commented
    February 17, 2017 09:52

    same here as described in the first comment

  • Tsviatko Yovtchev commented
    March 08, 2017 17:44

    This issue is caused by Fiddler Script Editor and happens only in pre-2017 versions of Fiddler. The 2017 version should not exhibit this problem. A clean install including removing any old FSE installs is needed though. Please, note that 2017 version of Fiddler include FSE and it is not available as a separate add on any more. Please, do not install any old versions of FSE add on on top of 2017 Fiddler.

  • Guest commented
    April 19, 2017 06:56

    As per Tsviatko Yovtchev comment, the issue seems to be resolved.

    Uninstall the current fiddler and install the new version. Seems to be working fine.

  • Aaron Roberts commented
    June 08, 2017 13:37

    This started happening for me when I enabled the 'Participate in the Fiddler Improvement Program."  Disabling this feature resolved the issue.