Works fine here for me on Linux.

Reset the page zoom on pages that cause problems.

• View > Zoom > Reset (Ctrl+0 (zero); Command+0 on Mac)

• http://kb.mozillazine.org/Zoom_text_of_web_pages

See also:

• http://kb.mozillazine.org/Websites_look_wrong

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Resetting zoom and starting FF in safe mode did nothing for me here (Firefox 21.0, Ubuntu 13.04). The outsized header problem continues.

Can you attach a screenshot?

• http://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.

You can try to use the built-in inspector via the right-click context menu to see if that helps to find out what is going on.

Here it is. Zooming up or down makes no difference; the broken layout shrinks or expands proportionately. And, a reminder, the image actually is the correct size for the layout--it is not too large.

Thanks for looking into this.

Is the image larger or is the other content smaller if you compare this with another browser?

The image displays correctly in both Chrome and Opera on Linux.

It also displays correctly in Firefox on OS X and Windows, as well as in IE (Windows), Chrome (OS X & Windows), Safari (OS X & Windows) and Opera (OS X & Windows).

It is only Firefox on Linux that is a problem.