To open the home page with a gesture, when it is set to "Firefox Home" (=about:newtab, aka what you see when opening a new tab by default) do this:
Add-Ons>Extensions>Foxy Gestures>Options>User Scripts (accept the warning)
Record the gesture in the left box
Paste this in the right box (also give the script some name):

executeInBackground(() => {
getActiveTab(tab => browser.tabs.create({
index: tab.index + 1,
active: false
}));
getActiveTab(tab => browser.tabs.remove(tab.id));
}, [ ]);

You're welcome.

PS: the developer of this extension should add this as a workaround to this limitation of WebExtensions.