Once this extension added to your Google Chrome browser, navigate to chrome://apps or click Chrome App Launcher next to Windows Start button.
This extension will be very helpful when you would like to test some changes done in Salesforce and it may effect in Salesforce1, or you need to demo Salesforce1 app but you do not have the devices.
Click above icon, a new window will be open to prompt you to enter your Salesforce login credential (depend on instance you would like to work on).
NOTES as of now, there are 2 things that you need to configure in Salesforce to make this extension works:
1. Enable Lightning Experience
2. From Setup | Apps | Mobile Apps | Salesforce1 Settings, select "Enable the Salesforce1 mobile browser app".
Type: Google Chrome extension
Production / Developer - https://chrome.google.com/webstore/detail/salesforce1-simulator/cknbjckicenodbiaejbmkjhldffonggp
Sandbox - https://chrome.google.com/webstore/detail/salesforce1-sandbox-simul/mgknkgnenlhghpfpdcohmgiejlcaapih
Blog last updated: 22 Aug 2016