Hey guys, I was having this exact problem with Firefox (version 70.0.1) and Chromium (version 78.0.3904.70) with Enpass version 6.2.0 (537). I found a solution that worked for me buried in the official user guide located here (https://www.enpass.io/docs/manual-desktop/browser_ext_setting.html#creating-keyboard-shortcut). Following the guide for Firefox was weird, but I figured out, changed the shortcut, and have had no issues since!
P.S. My OS is Kubuntu 18.04.3 LTS but I really don't think that should matter at all. I mention it in case you're at your wits' end and think that information might be useful.
