Page Loading Twice in FireFox (ASP.net)

Last week I found that my debugs are getting real slow for ASP.NET we Application on VS2005. during a debug issue I had a breakpoint on Page_Load event. The event was wired up to Auto. I always use FireFox as my default browser in VS2005 ( For I believe if ASP.net Page works in FireFox it will work in IE). Every time I visit a page during debug Page will be loaded twice.

Everything worked fine in IE 7 and Google Chrome.

As the application being maintained was relatively big I created a new webapplication with just default page and added a label to it. The same issue was being notices in the new application.

I tried the following from the answers and searches on web:

Changed
AutoEventWireup to "false"
Changed
EnableViewState to "false"
removed

set
EnableViewState of Label to "false"

removed
label

Downgraded
FireFox from 3.0.10 and tested on versions from 3.0.3 to 3.0.8

Nothing worked.

After three days and Weekend with Black Label, I was beginning to lose hope when today morning I got things working ( Hangover effect).
The only thing I had to do was remove
xmlns=http://www.w3.org/1999/xhtml
from
html tag.

I checked back by going back to default state of the form
AutoEventWireup to "true"

EnableViewState to "true"

Adding DOCTYPE

FireFox version 3.0.10

and page loaded just once.

I guess I now have to remove it from master pages in my original application.

One thing that still concerns me is how come things were working fine 10 days ago and what is the actual cause of this issue.???

my post on ASP.NET forum

http://forums.asp.net/p/1429154/3202335.aspx#3202335

Thank you,