There are way too many Tumblr themes out there now that are way too slow to load and navigate. If you’re going to make it pretty, at least make it a little bit performant. And when you pick a theme to use, please pay attention to how well it runs in your browser.
I mean, it’s just images and text on a background that’s white more often than not. There’s no reason to make it run like a Flash app.
If some themes bother you, you can switch your user agent to a mobile browser in order to load the smartphone theme.
I use this tool on Firefox: https://addons.mozilla.org/en-US/firefox/addon/user-agent-overrider/
When will you ever stop using Firefox and become part of the Chrome masterrace, Clare?