Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Try Restore Default on the customize page.

• https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars

Hello, I have run Firofox in safe mode. The problem remains unchanged.

I do not like so much to reset Firefox to default settings, otherwise I would lose all customizations. The reset cannot be undone with one click.

Best regards from Germany

I'm not sure what I see. This looks like the Bookmarks Toolbar with some other toolbar buttons placed on it, but you mention the overhsng menu. Do you mean the chevron '>>' as this would normally display items vertically and not horizontally ?

Note that I meant to refer to the "Restore Default" button at the bottom of the customize page and not to the Firefox refresh feature that creates a new profile. If you click this button then the label changes to "Undo".

This was mentioned in the community discussion forum (quote) Firefox 110.0.1 will cause about a 500px wide gap at the left end of the Bookmarks Toolbar if the user has removed the "Bookmarks Toolbar Items" control.

This will be fixed in a future Firefox release, currently version 112. Related bug report: Bug 1819980 110.0.1 misplaced icons in toolbars with no "Bookmark toolbar items"