Safari no longer defaults to typing in address bar. Why? I recently deleted cookies and deleted my AdBlocker for Safari. Since then, things have been acting weird, e.g. websites open slowly, my homepage was set to Yahoo, etc.

Previously, when I would open a new tab, the cursor would be in the address bar. Any typing I would do would start there. Now, I must manually click the address bar, or use the Command + L shortcut to go there. 

That's a pain. How could I reset this? I see nothing in Safari's Preferences.
Your system could have been infected with adware and/or malware. See this Apple Support page on how to remove adware.

For malware, I have relied on Sophos' free Antivirus for Mac for several years. I use it on my home machines, and my school uses it enterprise-wide on all Mac and Windows desktops, laptops and servers.