Few suggestions:
You are using a variable “albacross_drupal_trackid” whic...

Few suggestions:

1. You are using a variable “albacross_drupal_trackid” which will reside in the database. It would be great if you delete this variable when the module is uninstalled.
2. From the hook_help and comments in the .module file, I got that the script will be added in the footer. It would be great if you share this information in README.txt file and on the project page as well.
3. In the hook_form_validate, I don’t see the appropriate messages as per your logic. For example:
   if (!is_numeric($trackId)) { form_set_error('albacross_drupal_trackid', t('You must enter correct Track ID for your Albacross account')); }

   Here, probably “Please enter numeric tracking id from your Albacross account.” would be more clear to the user.

   Similarly,

   elseif ($trackId <= 0) { form_set_error('albacross_drupal_trackid', t('You should not use minus in front of your Track ID')); }

   This message would show in the case of zero(0) tracking id. So you can change it to like “Non-negative tracking id is not allowed."