When I open Firefox and click the search area (top right) and start to enter a search term, as the home page loads up the cursor moves to the search area of the web page before I have completed timing. How do I stop this?

My default search is Google (the top right space where you can click and select youtube, wiki etc. instead). When I open FF and my home page is opening (Yahoo) I start to either type a URL in the url area, or a search in the search area, and as the web page opens fully the cursor moves to the Yahoo search mid typing, meaning I search on half a word using yahoo when I want to use the url bar/google search area. Can this be stopped?