Windows 7: Chrome displaying certain pages in italics (e.g. Google), Firefox displaying bold

I cannot figure the exact cause, but today my browsers started displaying web pages oddly - many Firefox pages were in bold font and many Chrome pages in italic font.

Turns out I'd somehow lost the Arial system font.  On Windows 7 take a look at Control Panel -> Appearance and Personalization -> Fonts.  In the Arial directory I had Arial Black, Bold, Italic, Narrow, etc... but no Arial Regular. I assume Firefox and Chrome were substituting the bold and italic fonts for the missing regular font.

Not certain this is the ideal solution, but it worked for me.  Run this update:
http://www.microsoft.com/en-gb/download/details.aspx?id=16083
Arial Regular was now back in Fonts directory and all was well after restarting the browsers.