Tried to use with the Simple Tab Groups add-on (with additional STG plugins such as 'Create New Tab'). However, after opening a STG group into the sidebar and then clicking on the 'Open new tab' button, whatever happens to be the current highlighted tab, is *overwritten* with the defined homepage URL - and a real new tab (blank!) appears below. I have tried a different new tab homepage add-on [New Tab Override (WebExtension), by Soren] which does work as you would expect. Using latest Firefox (v70.0.1) as of this date [2019-11-15].