sforce is not defined in winter 16

Switching agent of your browser can easily load the emulator (remember don't need to enable Lightning for this, neither sharing rule), you can change browser agent in chrome/safari manually, or simply use agent-switch plugin to change agent to mobile

Agent Switch: (https://chrome.google.com/webstore/detail/user-agent-switcher-for-c/djflhoibgkdhkhhcedjiklpkjnoahfmg?hl=en-US)

and using this URL (enter your domain): DOMAIN.lightning.force.com/one/one.app

reference: http://www.oyecode.com/2015/10/winter-16-fix-salesforce1-oneoneapp.html

The one/one app is no longer available for Salesforce1 as of Winter16. See the Release Notes. You'll need to use an emulator as discussed in the notes. In my experience, you can typically use Chrome in mobile mode device emulation mode for most of your needs, but I've not used it recently to see if it's still working for non-lightning pages.

I found a very nice tool that replaces the one/one.app to test for mobile visualforce page on the web. It is actually a plugin on chrome web store name salesforce1 simulator. From there it works like a charm. But i can't debug the code if the js crashes. Then i do as suggested, using an emulator on my chrome browser, then i launched the one/one.app (no lightning in the url) and inspect using the chrome inspect element.