One day, I decided to conduct an experiment using Google and Firebug. With my firebug open, I typed "in" into the search bar on Google. To see what was happening behind the scenes, I checked the "NET" tab in Firebug and noticed that several new GET requests had been sent out to retrieve a list of search autocomplete suggestions.
For example:
GET http://clients1.google.com/complete/search?hl=en&client=hp&expIds=17259,17315,23628,24549,26637,26761,26849,26869,27386,27404&q=i&cp=1
Surprisingly, these requests were categorized under the "JS" section in Firebug, rather than appearing as XHR (XMLHttpRequest). This made me wonder - isn't Google actually sending AJAX GET requests in the background?