javascript aggregation disables the font-your-face module and views-slideshow on the main page
It turned out the problem is with the fields slideshow module and its use of js/jquery libraries.
I've realised that JS error happens  after calling some slideshow libraries, so i googled for aggregate js / field slideshow.
As per https://drupal.org/comment/7874537#comment-7874537 , I used the 2.1.x version of the imagesloaded library and everything worked nice afterwards.