Hi Katie,
The same problem exists in Opera. "-)
I don't use the PayPal function so I can't point you to the exact file you need to change, but find the file that creates this piece of generated text:
<!-- ** BEGIN PAYPAL EXPRESS CHECKOUT ** -->
<div id="PPECbutton" class="buttonRow">
<a href="http://www.ktnaturals.com/ipn_main_handler.php?type=ec"><img src="\includes\templates\custom\buttons\english\btn_xpressCheckout.gif" alt="Express Checkout - Requires a credit card or Paypal account" /></a>
</div>
<!-- ** END PAYPAL EXPRESS CHECKOUT ** -->
And change the \ to /.
The place to start your digging is [include(DIR_FS_CATALOG . DIR_WS_MODULES . 'payment/paypal/tpl_ec_button.php')].
IE ignores/corrects errors like this, but other browsers require compliance and won't ignore these kind of errors.
That fixed it in Opera; my experience is that if it works in Opera it will work in FF.
Hope that helps!
Becky



