I misunderstood, I thought that it was the shadow giving you problems.

FF and IE are both hard with floats and centers in a nested div situation. Actually, I'm surprised: margin: 0 auto has always worked with FF but not IE.

Have you tried adding "text-align: center"? to .content and then text-align:left to the inner boxes?

To tell you the truth, to get cross-browser compliance, I just approximate left margins to internal boxes (especially in float situations) and have alternate style for other browsers if there are differences.