Type about:preferences#general<enter> in the address bar.

There are two settings;

• When Firefox Starts

When the browser is started, what do you want to display? Many of us choose Show My Home Page.

• Home Page

When a new page is opened, what do you want to be displayed?

1. Use Current Page. Use what ever page(s) are open at that time.
2. Use Bookmark
3. Restore To Default. about:home shows a Mozilla home page with tools.

You can use any of these that you wish;

about:home (Firefox default home page), about:newtab (shows the sites most visited), about:blank (a blank page),

or you can enter any webpage or about: page you want.

In case you use "Clear history when Firefox closes".

• do not clear the Browsing History

• Options/Preferences -> Privacy -> Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/kb/remove-recent-browsing-search-and-download-history

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing cookies will remove all selected cookies including cookies with an "Allow" exception you may want to keep