Screenshots in Firefox add-on

[Arcopix]

Creating screenshots in Firefox add-on results in an error:

TypeError: window.event is undefined[tools.user.js:2576:9](moz-extension://87245fb8-5f9f-456c-80b4-f221fb619808/tools.user.js)
    generateScreenshot moz-extension://87245fb8-5f9f-456c-80b4-f221fb619808/tools.user.js:2576
    <anonymous> moz-extension://87245fb8-5f9f-456c-80b4-f221fb619808/tools.user.js:486

Related code:

    if (window.event.ctrlKey) {
        hook = false;
    } else {
        hook = localStorage.getItem('cfgDiscordTokenA');
    }