I'm not a huge fan of the trend of putting (sometimes multiple) fixed-position, floating bars on web sites. I'm sure there are browser extensions that get rid of them, but in mobile Safari, where the screen space they take up is most precious, that isn't an option. Here's a js bookmarklet that gets rid of anything with position:fixed
javascript:var%20nodes%20=%20document.querySelectorAll('*');for%20(var%20i=0;%20i%3Cnodes.length;%20i++)%7B%20var%20node%20=%20nodes%5Bi%5D;%20var%20style%20=%20getComputedStyle(node);%20if%20(style.position=='fixed')%20%7Bnode.style.position='absolute'%7D%7D
(except, mysteriously, on the tumblr mobile site, where some floating buttons survive. Anyone know why?)