Technically, setting your font to be eg 14 points, should be an absolute size - the same font should be the same dimensions (in mm/inches) on all displays. Now, you probably hold your smartphone closer to your face than you sit to your 30" LCD screen -- so that might not really be what you want (same font size on your phone and on your desktop screen).
Additionally this only works for scalable graphics -- which is why Apple went trough such hoops to make retina displays usable -- quadruple the dot pitch on screens, and all icons and bitmaps become miniatures.
Personally I just use the browser zoom-function -- I find most sites use too small fonts, and end up with too wide text columns (which is somewhat alleviated by not browsing full screen, but in a "long" window).
Anyway, the following might be of interest:
Xorg, dpi: https://wiki.archlinux.org/index.php/Xorg#Display_Size_and_D...
Windows (8) dpi/zoom: http://nvidia.custhelp.com/app/answers/detail/a_id/3153/~/ad...
Some notes from Microsoft on writing DPI-aware applications: http://msdn.microsoft.com/en-us/library/dd464646(VS.85).aspx
Android does not have this problem since devs always use dp (density independent pixel) as units of measurement and OEMs choose good DPI values when they are releasing devices.
Although less gracefully, iOS solves this problem too (by doubling the resolution and scaling everything by two).
Also does the zoom level in your browser affect the resolution of videos/images? It seems like it would.