As a Firefox support volunteer, I'm here to help you with your question. To have Firefox open automatically when you start your computer, you can follow these steps:

Open Firefox and click on the menu button in the top-right corner (it looks like three horizontal lines). From the menu, select "Options" or "Preferences" (depending on your operating system). In the General tab, scroll down to the "Startup" section. Check the option that says "Restore previous session" or "Restore previous windows and tabs" (the wording may vary slightly). Close the Options or Preferences tab. With this setting enabled, Firefox will remember your open tabs and windows from your previous session and restore them the next time you start the browser.