1366*768 is in fact a pretty common resolution. A lot of 14" and 15.6" laptops from the past 10 years have it. Nowadays it is becoming less common as 1920*1080 is starting to be the standard. I would say check the browser version, install it and try if you can replicate the problem. I don't know wheter Windows scaling might have something to do here. It is usually disabled with those resolutions.