Single post thumbnails, and image or post title hover on homepage or posts list

When I visit my site for the first time, e.x after cleaning caches and cookies on my browser, on the homepage, on post title hover the font family changes to a different font. And my second problem is, how to make thumbnails on single post, full size and with the highest quality. You can see on my site http://directionstone.mesoshqip.org that I have made thumbnails show full size, but their quality is low, if I click on the image, the image opens in light box with the same or bigger size, but it has higher quality. How to make these full size images be of high quality like them on the homepage featured.