Is this a toolbar that shows in the toolbar area at the top of the browsing window?

If the toolbar is added by an extension then best is to uninstall the involved extension.

• https://support.mozilla.org/kb/disable-or-remove-add-ons
• https://support.mozilla.org/kb/uninstalling-toolbars
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

You can use one of these to set which toolbars to show.

• "3-bar" menu button -> Customize -> Show/Hide Toolbars
• View -> Toolbars
  You can tap the Alt key or press F10 to show the Menu Bar
• Right-click empty toolbar area

Can you attach a screenshot if the above doesn't work?

• https://en.wikipedia.org/wiki/Screenshot
• https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

• use a compressed image type like PNG or JPG to save the screenshot
• make sure you do not exceed the maximum size of 1 MB

Thank you for sharing your Firefox configuration data. It shows this extension:

• EasyPDFCombine

cor-el already linked to articles providing steps for removing unwanted extensions, but I think this confirms that would be the best place to start.

If the extension also changed your home page (the one that appears in new windows and when you click the Home button on the toolbar) or default search engine, please see these articles to set them back to your preferred sites:

• How to set the home page
• Change your default search settings in Firefox