I am playing with chrome extensions, my manifest loads a background page with:
...
"background": { "scripts": ["background_page.js"]
What you are using is an Event Page(background_page.js). Event pages are unloaded when the browser detects that the page is not doing anything. So what's happening is that when you open a new tab, the Event page is being reloaded and starts executing from the top again. This way chrome is able to have your app use less memory and speed up the browser.
If you want to fix the problem simply use persistent:true
which will make sure the page "persists" indefinitely or until the user closes the browser. If you would really like to keep your app efficient with memory, you should take a look at the runtime.onSuspend
method which gets called each time your Event page unloads. This way you can save stuff before the page gets unloaded so that you can resume where you left off.