Prerequisites:

TamperMonkey (for Google Chrome) OR GreaseMonkey (for Mozilla Firefox) add-on has to be installed in your browser. Seriously, script won't work without this add-on.

Also please take into account this script works only with English or Russian versions of LinkedIn.

How to install and use:

1. Visit GreasyFork
2. Click "Install this script"
3. Ready! Visit somebody's LinkedIn profile to check. Mine for example :)
   Note that person you want to endorse has to be in your contacts list!