I use the NSS certutil tool from Mozilla to install a certificate in Firefox: https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/tools/NSS_Tools_certutil The commands are listed in the link. Someone used with certificate and commands should be able to understand my problem. From the parameters I use, the following (I indicate the reason for, because I may be wrong): -A : so if the cert8.db doesn't exist, it creates one. -n : for this one I don't understand. From my understanding this should be the same as -i? So I set the same thing -i : certificate name + location -t : truast arguments -d : path + name of certificate database So my code is the following: set cert8dbPath=%userprofile%\Application Data\Mozilla\Firefox\Profiles\%randomalphanum%.default\cert8.db set certName="FiddlerRoot.cer" certutil.exe -A -n "%certName%" -i "%certName%" -t "TCu,TCu,TCu" -d "%cert8dbPath%" I got this error, any idea? certutil.exe: function failed: Failure to load dynamic librarty error 126