I know this can most probably also be considered a "google software" problem. But it's happening in FF only. FF: 59.0.1 How I reproduce: Go to wikipedia.org, copy a text, paste it somewhere else (in gedit for instance). Result: it works! Go to inbox.google.com, or docs.google.com (a spreadsheet for instance), and hit ctrl+c. It assumes you hit only "c". In inbox for instance, it assumes you want to "compose" as a result. Working workarounds: right click -> copy in FF, or ctrl+c in Chrome. I have already tried the usuals (reboot, safe mode, in cognito mode), and none of them have solved the issue.