Question: When I see page source of a website, I can know that a website is running Magento, but how do I know the extensions installed on that store? Is it possible to know from the page source?

EDIT: more information

The site I'm Interested is: <http://www.jiayumobileshop.com/>

I wanted to know what extensions and themes they are using in that site, **esp** See the Right hand side-Bar Slider, Contacts and Login.

Answer: 
A great way I can think of is to check for their XML files in `app/etc/modules`

```
app/etc/modules$ ls
Aschroder_SetStartOrderNumber.xml  GoMage_Checkout.xml            Minerva_Shipping.xml
Aschroder_SitemapSubmit.xml        GoMage_DeliveryDate.xml        Phoenix_Moneybookers.xml
Aschroder_SMTPPro.xml              Indust_CustomShippingRate.xml  QAS_GlobalAddressVerification.xml
AW_Advancedreports.xml             Mage_All.xml                   Sebastian_Export.xml
AW_All.xml                         Mage_Api.xml                   TBT_Enhancedgrid.xml
AW_Blog.xml                        Mage_Bundle.xml                TinyBrick_OrderEdit.xml
AW_Mobile.xml                      Mage_Centinel.xml              TM_EasyCatalogImg.xml
Dull_Uploader.xml                  Mage_Compiler.xml              TM_EasyLightbox.xml
EM_DeleteOrder.xml                 Mage_Connect.xml               TM_Easyslide.xml
Find_Feed.xml                      Mage_Downloadable.xml          TM_EasyTabs.xml
Flagbit_ChangeAttributeSet.xml     Mage_Weee.xml                  TM_Highlight.xml
GoMage_All.xml                     Mage_Widget.xml                TM_Templatea034.xml

```

Or if you can't get ssh access, upload this script as `var/export/_modules.php` and visit the according URL to get the same output. 

```
<?php
echo "<pre>\n";
$cmd="ls ../../app/etc/modules";
$output=Array();
$rtn=NULL;
exec( $cmd, &$output, &$rtn );
if(is_array($output) )
    foreach($output as $line)
        printf( "%s\n", $line);
?>

```
There is no Browser plugin that identify every exact plugin used on their site however if your familiar with plugins then your be able to identify that yourself, or if you don't know simply take a screenshot or URL link and post it on the Magento forums and I bet within a couple of hours someone gets back to you with an answer.