Edit in JSFiddle

function CheckForOther(item, origlen) {
    var sitem = item.options[item.selectedIndex];

    if (item.selectedIndex == (item.length - 1)) {
        var val = prompt("ADD A NEW CHOICE:", "");

        if (val === null) item.selectedIndex = 0;
        else {
            var slen = item.length;

            if (slen == origlen + 1) {
                item.options[slen] = new Option(sitem.text, sitem.value);
            }

            item.options[item.length - 2].text = val;
            item.options[item.length - 2].value = val;
            item.selectedIndex = item.length - 2;
        }
    }
}

function validateForm(theForm) {}

<div class="container">
     <h2>All Customers: Web Inquiries</h2>

    <form name=qdbform method=POST onsubmit='return validateForm(this)' encType='multipart/form-data' action=https://www.quickbase.com/db/bj3vc3z73?act=API_AddRecord&apptoken=cwfcy7gdzqrsyncqbi2bn4u4kr class="form-horizontal" role="form">
        
        <div class="form-group">
            <label class="control-label col-sm-2" for="_fid_6">Name:</label>
            <div class="col-sm-10">
                <input type="text" class="form-control" id="_fid_6" name="_fid_6" placeholder="Enter Name">
            </div>
        </div>
		
        <div class="form-group">
            <label class="control-label col-sm-2" for="_fid_7">Company:</label>
            <div class="col-sm-10">
                <input type="text" class="form-control" id="_fid_7" name="_fid_7" placeholder="Enter Company">
            </div>
        </div>
		
        <div class="form-group">
            <label class="control-label col-sm-2" for="_fid_8">Email:</label>
            <div class="col-sm-10">
                <input type="email" class="form-control" id="_fid_8" name="_fid_8" placeholder="Enter Email">
            </div>
        </div>
		
        <div class="form-group">
            <label class="control-label col-sm-2" for="_fid_9">Phone:</label>
            <div class="col-sm-10">
                <input type="phone" class="form-control" id="_fid_9" name="_fid_89" placeholder="Enter Phone">
            </div>
        </div>
		
        <div class="form-group">
            <label class="control-label col-sm-2" for="_fid_11">Company:</label>
            <div class="col-sm-10">
                <input type="text" class="form-control" id="_fid_11" name="_fid_11" placeholder="Enter Company">
            </div>
        </div>
		
        <div class="form-group">
            <label class="control-label col-sm-2" for="_fid_12">State:</label>
            <div class="col-sm-10">
                <select class="form-control" name="_fid_12" id="_fid_12" onChange=CheckForOther(this,5)>
                    <option>QLD</option>
                    <option>VIC</option>
                    <option>NSW</option>
                    <option>WA</option>
                </select>
            </div>
        </div>
		
        <div class="form-group">
            <label class="control-label col-sm-2" for="_fid_13">Inquiry Type:</label>
            <div class="col-sm-10">
                <select class="form-control" name="_fid_13" id="_fid_13" onChange=CheckForOther(this,4)>
                    <option>Sales</option>
                    <option>Service</option>
                    <option>Tech Support</option>
                </select>
            </div>
        </div>
		
        <div class="form-group">
            <label class="control-label col-sm-2" for="_fid_14">Product Interested In:</label>
            <div class="col-sm-10">
                <input type="email" class="form-control" id="_fid_14" name="_fid_14" placeholder="Product Interested In">
            </div>
        </div>
		
        <div class="form-group">
            <label class="control-label col-sm-2" for="_fid_14">Message:</label>
            <div class="col-sm-10">
                <textarea class="form-control" rows="5" id="_fid_10" name="_fid_10" placeholder="Enter Message"></textarea>
            </div>
        </div>
		
		<button type="button" class="btn btn-primary">Save</button>
		
        <input type=hidden name=rdr value='http://www.countrysolar.com.au/contact/thank-you'>
		<input type=hidden name=fform value=1>
		
    </form>
</div>