https://support.mozilla.org/en-US/kb/how-to-set-the-home-page

Type about:config<enter> in the address bar. If a warning screen comes up, press the I Accept the Risk button. At the top of the screen is a search bar. Type browser.startup.homepage

What is the value? Right-click and select Reset to restore its default value; about:home

after browser.startup.homepage entered, this came up: browser.startup.homepage;about:home browser.startup.homepage_override.buildID; browser.startup.homepage_override.mstone; services.sync.prefs.sync.browser.startup.homepage;true I clicked on each one and hit 'reset' on the right click. Not clear on what to do with the instruction: about:home

If these pages aren't set as multiple homepages then you might have a problem with sessionstore.jsonlz4 that stores session data (open tabs)

You can check that those pages aren't set as multiple homepages.

• Options/Preferences -> Home: Home

Firefox supports multiple homepages separated by '|' (pipe) symbols.

You can check for problems with the sessionstore.jsonlz4 file in the Firefox profile folder that stores session data.

• delete sessionstore.jsonlz4 and sessionstore.js

When sessionstore.jsonlz4 is deleted you lose pinned tabs and open tabs and you will have to recreate them, so if necessary make a note or bookmark them.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/Profiles