Safari

Check Safari/Preferences/General to see if there is a Safari opens with option. If there is, set that to All windows from last session.

If you don't see that option, try going to System Preferences/General and uncheck Close windows when quitting an app. Quit/reopen Safari and check for the Safari opens with option.

If you quit Safari with various open tabs, the next time you reopen it select History -> Reopen All Windows from Last Session to resume the last used tabs.

There's even a paid Safari extension to manage browsing sessions: https://sessionrestore.sweetpproductions.com

Funny you should say you were having some issues with Safari. I was also just the other day. I use Google Chrome for most of my internet needs. However the other day I wanted to open safari for something. I don't remember why I did open it. However when I opened it a page that I had used a year ago came up as the default web page. It took me 3 try to get this changed do the the fact when I put in the page google.com that I wanted Safari to open to it kept changing to the page I had used 3 years ago. After the 3 try and a little cursing at the computer it finally changed.