Safari can't load specific websites

Hello everybody,

so for the past couple of weeks I've been experiencing the following problem: on both my iMac late 2010 and Macbook Air 2009 Safari is unable to load / connect to certain websites (about 20-30% of the pages I visit). If I try navigating to a specific page, I often get the "can't find server" error message. The websites Safari can't open seem to vary randomly - I might suddenly find myself unable to access a page that worked perfeclty fine a minute ago, and vice versa. De- and reactivating WiFi sometimes helps, sometimes it doesn't.

Also Safari at times loads websites incompletely, with the entire website format distorted and all images missing, replaced by those blue "?" symbols.

What is interesting though is that I do not experience these problems when opening the very same websites at the exact same time using another browser, such as Chrome or Firefox.

I already reset Safari and emptied the cache, deactivated all addons / plugins and made sure that both my OSX and Safari are the latest version available. I'm at a loss here - at first I thought it might be a general internet / wifi problem, that was until I found out that everythings works just fine with other browsers.

I hope you guys can help me! Of course I could just switch to Chrome or Firefox, but in my opinion Safari is vastly superior to these two so I'd really prefer keeping Safari.