Thank you, but technically you don't need an extension.
1) Go to
Sign In , or any page on the steampowered domain,
2) on steam db, search for the subid of the package to add ( steamdb->packages->SUBID), it's a 6 or less digit number. It obviously works just with free stuff. Look for "No Cost" or "Free On Demand" packages. If there are multiple free packages, try them all, often they are regional packages.
3) open a browser console (F12 on PC, go to the console tab)
4) in the browser console, paste and run with enter:
JavaScript:
jQuery.post('//store.steampowered.com/checkout/addfreelicense',{action:'add_to_cart',sessionid:g_sessionID,subid:SUBID_FROM_STEAMDB});
alternate method:
JavaScript:
AddFreeLicense(SUBID_FROM_STEAMDB, 'game')
In alternative to step 3 and 4, you can also use a bookmarklet like:
JavaScript:
javascript:var e="", r=""; /expression evaluate the result/do{/display expression and result and ask for a new expression/e=prompt("Enter game SubID:"+e+"\n"+r+"\n", e);try{r="Result:"+jQuery.post('//store.steampowered.com/checkout/addfreelicense',{action:'add_to_cart',sessionid:g_sessionID,subide)});} /try to evaluate the expression/catch(ex){r=ex;}} while(e); /continue until no expression entered or cancel clicked/void 0;
(just create a new bookmark and add this as address)