Easy Checkbox Checker

This extension would toggle the checked status of all checkboxes between the first and second clicked checkbox.

Usage Instruciton:
1. Click on the extension icon from the browser toolbar
2. select the beginning and ending of the list of checkboxes to check or uncheck
3. keep selecting like step 2 or click the icon again to exit the selection mode

Note：
If the extension is not working after a click, try disabling all other extensions,try again, and reenabling them. There is a common error where the background could not establish the connection to content script. After some research, i think this is the best approach available. Will keep tuning it and make a fix once a better one is found.