Font size difference Firefox IE <p> only

[fruitgum]

I have finally managed a page with CSS layout BUT ...
While header text fonts are exactly the same in IE and Firefox, all the text is much smaller in Firefox than IE. It's messing up my layout, the difference is quite large.
My text size is set as 62.5% in body. Then all text sizes are in ems.

is 1.2em with line height 130%.
H1, for example, is 2.7em.
Headers are Trebuchet, p is Verdana.
In IE on my pc text size is medium. I can't see where you change it in Firefox but I certainly haven't changed it from default and anyway the headers are fine.
So what's happening?
I've checked carefully and can see no other styles which might interfer unless the (DW CS4 Spry) menu bar does - it has "font 100%".
Any ideas?

[colweb]

I presume IE and Firefox are both run on the same machine? There can be a significant difference in layout when you see the site with IE or Firefox on Windows and then look at it in Firefox on a Linux machine.

Do you have firebug installed in Firefox? If not, install it and inspect the actual size of the text inside your tags. Firebug can also tell you what styles are inhered from css. Might give you a clue why there is a difference with IE.