Remove Drupal.edit.util.stripPX() in favor of parseFloat().

/**
 * Strip extraneous information ("px") from a given value in preparation
 * for getPositionProperties().
 */
Drupal.edit.util.stripPX = function(value) {
  if (value) {
    var index = value.indexOf('px');
    if (index === -1) {
      return NaN;
    }
    else {
      return Number(value.substring(0, index));
    }
  }
  else {
    return NaN;
  }
};

Feels a lot like you're trying to do what the native parseFloat does.

Also, it's generally advised to not use primitive constructors like Number() as they cause unnecessary overhead and can sometimes lead to getting a different type than you expected.

Attached patch removes the stripPX method and replaces all occurrences with parseFloat.