Navigate to Tools > Telerik Fiddler Options > HTTPS> Actions > drop down.
you'll an enabled option to "Open Windows Certification Manager". Not
really, on Linux or at least not a Windows one. You can choose and click
the option which then results in the following output on the console:
xdg-open: unexpected argument 'certmgr.msc'
Try 'xdg-open --help' for more information.
Running Fiddler v18.104.22.168842 on Ubuntu 16.04 with Xfce4 window manager.