JavaScript Problem in Firefox 4.0

I have some problem regarding JavaScript compatibility. I am using below code to clean text box blur data when click on that Text Box.This code is working fine in Firefox 3.6 & IE, but not supportable on Firefox 4. Some errors are there in error console like clearTextFrom is not defined & clearTextTo is not define. Please check below code & suggest me how can i run this code on FF4.

function clearTextFrom() {
    if(document.getElementById("size_from").value=="From Year")
        document.getElementById("size_from").value="";
}

function clearTextTo() {
    if(document.getElementById("size_to").value=="To Year")
        document.getElementById("size_to").value="";
}

Waiting for your quick response.

Thanks in Advance Tanu

EDIT:

<div class="yearsearch"> 
<input type='text' style='width: 60px;' name='size_from' maxlength='4' size='17' id='size_from' onfocus='clearTextFrom();' onkeyup="validNumbers(document.getElementById('size_开发者_JAVA技巧from')); sync();"/> 
<input type='text' style='width: 60px;' name='size_to' maxlength='4' size='17' id='size_to' onfocus='clearTextTo();' onkeyup="validNumbers(document.getElementById('size_to'));"/>
</div> 

This is the code which i am using to call these functions.

---

Change to this :

<script language="javascript">
    function clearTextFrom(item) {
        if(item.value=="From Year")
            item.value="";
    }

    function clearTextTo(item) {
        if(item.value=="To Year")
            item.value="";
    }
</script>


<div class="yearsearch"> 
<input type='text' style='width: 60px;' name='size_from' maxlength='4' size='17' id='size_from' onfocus='clearTextFrom(this);' value="From Year"/> 
<input type='text' style='width: 60px;' name='size_to' maxlength='4' value="To Year" size='17' id='size_to' onfocus='clearTextTo(this);'/> 
</div>

in this code you are sending each textbox to related function. I tested and worked for me in FF4.0

sample : http://jsfiddle.net/fkP2P/