Lato font broken in FF when using latin-ext characters

I have developed a site in Polish using the 'Lato' Google Font (supports the latin-extended character subset). My site is http://www.innova.uno I have placed the code from GF website in my theme's ` section:

<link href="http://ift.tt/2i37O6t" rel="stylesheet">

When I open the site in Chrome, all text are displayed correctly. But when opening the site in Firefox the Polish characters are changed to Times New Roman - but only in the Lato font based texts - headers (see screenshot: http://ift.tt/2COwpWL) - other latin-ext fonts work well.

I don't know if any of you will see the site in FF the same way, but if anybody does and could have a slight idea why is this happening - please give me a hint! :) Thx.