In the about:config you should be able to add a custom url for new tab. https://www.howtogeek.com/333805/how-to-change-or-customize-firefoxs-new-tab-page/ http

In the about:config you should be able to add a custom url for new tab. https://www.howtogeek.com/333805/how-to-change-or-customize-firefoxs-new-tab-page/ https://www.howtogeek.com/333805/how-to-change-or-customize-... This site shows the steps. I tried it and mine is working. Firefox Developer Edition.