Hi @Anshu kumar,
trying to get the Enpass extension to work with Firefox under Linux, I face the same issue. I can confirm that the file .mozilla/native-messaging-hosts/EnpassNMHost.json exists on my machine, is world-readable and that the path in the file is correct. I can also confirm that EnpassHelper is successfully started by Enpass, and I can see a EnpassNMHost process for some time. So at first glance, everything looks fine, however I get the Enpass Connection Error when clicking on the icon.
What I noticed, which might be helpful: when I start firefox from the commandline, I can see this error message being printed:
This seems to be coming from the Enpass extension, AFAICT... Clearing the directory .mozilla/firefox/*.default/storage/temporary/moz-extension+++d35a2cae-4679-4b23-bc27-df6cda4eeeef/ did not change the behavior, neither did creating a managed-storage JSON...
Gentoo Linux amd64, Firefox 62, Enpass 5.6.9 with browser extensions enabled, Enpass Extension 5.5.2.