Safari won't open, period. Though I just quit it a second ago and wanted to re-open it.

We're all having the same issue tonight. Take a look at all the threads below yours...

:(

You are welcome.

See if anything here helps.

https://discussions.apple.com/thread/250021459

https://discussions.apple.com/thread/8573312?page=2

Try setting up another admin user account to see if the same problem continues. Please post back on whether or not this worked. Also try the Safe Mode. Please post back on whether or not this worked.

Isolating an issue by using another user account 

Safe Mode - About

If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor.  Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.

Etrecheck – System Information

If the log won’t post, try posting it here and provide a link in a reply        Pastebin