Disable Firefox Close Other Tabs Warning

In Firefox there is not a "Don't ask again" check box on the Close Other Tabs warning dialog. Here is how you disable the dialog

    - Type about:config into the location bar and press enter
    - Accept the warning message that appears, you will be taken to a list of preferences
    - Locate the preference browser.tabs.warnOnClose, if its value is set to true, double-click on it to change its value to false
    - Repeat this for these 3 preferences browser.warnOnQuit, browser.warnOnRestart and browser.showQuitWarning

H/T to https://support.mozilla.org/en-US/questions/753984#answer-302390