Different Browsers are displaying HTML differently

I am working on some HTML code, its really old code so its not something I am really used to seeing. I made a small change to the code, moved the save button, but when I display it in each of the browsers im testing on, Firefox,Chrome,IE they all look different. Firefox is displaying it the way I want it to

But the other two are displaying the same page, with the same exact code incorrectly. IE

Chrome

Here is my code, please let me know what has gone wrong im not sure how to fix this is issue. Thanks!

    <div id="textdefaults" runat="server">
    <div>
    <asp:Button ID="btnSubmitTextDefaults" Text="Save" runat="server" Height="29px" style="margin-left: 900px" Width="64px" OnClick="btnSubmitTextDefaults_Click" OnClientClick="SaveLanguage();" />
    </div>
    <div class="aTab">
        <asp:UpdatePanel ID="upTextDefaults" runat="server" UpdateMode="Conditional">
            <ContentTemplate>
                <div class="aTab">
                <TagUpdate:TextDefaults id="myTextDefaults" runat="Server" />
                    <asp:UpdateProgress ID="UpdateProgress3" runat="server">
                        <ProgressTemplate>
                            <div class="progress">
                            <asp:Image ID="imgTextDefaults" runat="server" ImageUrl="~/Bannerlink/Images/ajax-loader-big.gif" />Saving...
                            </div>
                        </ProgressTemplate>
                    </asp:UpdateProgress>
                </div>
            </ContentTemplate>
            <Triggers>
                <asp:AsyncPostBackTrigger ControlID="btnSubmitTextDefaults" EventName="Click" />
            </Triggers>
        </asp:UpdatePanel>
    </div>
   <br />
</div>