Another missing cool feature from old Firefox for mobile was ability to remove a site url from suggest and history just by long touching on it, which seems to have entirely purged it from the places db.

In fact, the new one doesn't remove things from suggest even if you remove it from your browser history manually, which is also really only convenient to do if you accessed it recently. If you don't want things spamming up suggest, the only option is to use private browsing or wipe your entire history.

Click on the lock in the URL bar then "Clear cookies and site data"