The short answer to this question is to state our preference. The Firefox browser from Mozilla is standards compliant and has some really useful add ons. Because of this, it is the browser we have chosen to optimise MySiteAdmin for.
The longer answer is that, as a webmaster (or user of MySiteAdmin), you should be aware of how your website displays in a range of browsers. Internet Explorer is still widely used, but Firefox, Google Chrome and Safari are all catching up and you should be testing your website on these 4 browsers.
As stated, we use Firefox at Refractiv because it has excellent add ons - take a look at our Essential Adds Ons for Firefox feature - but Chrome and Safari are similar and all 3 are standards compliant, meaning that if your site works in Firefox it will work in Chrome and Safari.
In summary therefore, we recommend you download Firefox as a primary or secondary browser and use it as your MySiteAdmin browser. It is also good practice to check all new pages in Firefox and at least Internet Explorer 8.