Edit 2020/04/09 I have tested both text selection (shift + left / right arrow) and full text selection (shift + ctrl + left / right arrow), but for me it works fine with no issues on Mac and Windows.
Please try disabling your other add-ons and testing again or updating your browser to the latest version. ----
thanks for reporting the issue. try to update to v5.2.2 - Add-on keyboard shortcuts will not excute while focus on searchbox - Removed Youtube Hotkey listeners while using add-on keyboard shortcuts ( Youtube shortcuts will be automatically added back after command is done )
