If anyone is still looking for this fix, here is the solution: replace the _renderBorder function (in my installation, in ricoStyles.js file) with one which doesn't use innerHTML. This works for me:

_renderBorder: function(el,bgColor) {
var borderContainer = document.createElement("div");
var borderValue = "1px solid " + this._borderColor(bgColor);
borderContainer.style.borderLeft = borderValue;
borderContainer.style.borderRight = borderValue;
borderContainer.style.padding = "0px";
borderContainer.style.margin = "0px";

while (el.firstChild) { borderContainer.appendChild(el.firstChild); };
el.appendChild(borderContainer);
},

All credit to Lokkju (http://www.lokkju.com/) for posting this on the OpenRico forums:
http://weblog.openrico.org/index.php/archives/6