the toolbar as in the bar at the top of the screen that has the search bar, bookmarks and tabs, sorry if there is a better word for this

Make sure Firefox isn't set to run in Full Screen mode (press F11 or Fn + F11 to toggle; Mac: Command+Shift+F).

• https://support.mozilla.org/en-US/kb/how-make-firefox-and-websites-go-full-screen

When you are in Full Screen mode, hover the mouse to the top of the screen to make the Navigation Toolbar and Tab bar appear. Right-click empty space on a toolbar to find "Exit Full Screen mode" and "Hide toolbars".

You can use one of these to leave Full Screen mode:

• press the F11 key
• click the Maximize button at the right end of the Tab bar
• click the Full Screen button in the "3-bar" Firefox menu button drop-down list

You can run in Kiosk mode if you don't want toolbars.

You can possibly use code in userChrome.css to disable the #fullscr-toggler.

*|div#fullscr-toggler {display:none!important;}

• https://support.mozilla.org/en-US/search/?product=firefox&w=2&q=fullscr-toggler

More info about userChrome.css/userContent.css in case you are not familiar:

• https://www.userchrome.org/what-is-userchrome-css.html
• https://www.userchrome.org/how-create-userchrome-css.html
• https://www.userchrome.org/firefox-changes-userchrome-css.html

In Firefox 69 and later you need to set this pref to true on the about:config page to enable userChrome.css and userContent.css.

• about:config => toolkit.legacyUserProfileCustomizations.stylesheets = true
• https://support.mozilla.org/en-US/kb/about-config-editor-firefox