As Firefox does not have an email client built in, how are you checking your Outlook account? An add-on? I see a Lync plugin, but I'm not sure if that's for mail or not - internet search suggests it's an instant messenger thing. Check that it's up to date at https://www.mozilla.org/en-GB/plugincheck/ just in case, and try disabling it if it's up to date to see if that plugin is causing the errors. You can configure your Plugins, Extensions and Themes in '''about:addons''' (type it in like a normal web address) under their respective tabs.