How do you mean by too big? Are there many icons on the bar? Are they all needed?

I use two toolbars, a vertical bar, and the add-ons bar. All of these are available as add-ons.

Cannot see "File" and only part of "Edit". The vertical scroll bar on the right hand side is off the page.

I am referring to the menu bar.

It sounds like the Firefox window is too long horizontally. Grab a corner and move to closer to its opposite.

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

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

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