I googled it for you and I couldn't find a way of defaulting to a specific browser....I could be wrong though. But I do know the default browser that opens certain web pages/docs depends on what the person has set up in their settings...so I don't know if you can place a setting in the word doc that says when clicked on, open in this specific browser. Don't forget not everyone has firefox on their computers. Mac's come with safari by default and windows have Internet Explorer.