Firefox for Android doesn't have that function. You can set a custom home page and set Firefox to launch it in new tabs under menu > Settings > General > Home However, I'm not aware of any way to navigate the current tab to that page conveniently. There is an add-on but the reviews are so mixed I can't tell whether it is working properly in Firefox 57: https://addons.mozilla.org/firefox/addon/home-button-for-ff-on-android/