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You can always just have Torbit automatically apply these optimizations for you though.
1) Download all the CSS (and JS) in one request which reduces the number of round trips and resource blocking
2) It makes it easier to push the CSS into local storage which is dedicated space for the domain (we don't have to compete with resources on other sites for space in the web cache) and tends to stick around longer, so we don't have to download the resources on repeat visits as often
3) It allows us to load only parts of the combined CSS on other pages. If you include CSS files A, B, & C on the first page and only C & D on the second page the user visits we can download all three files A, B, & C in one request on the first page and then only download D on the second and still only apply C & D on the second page. It provides a lot of the benefits of splitting up your CSS into multiple files without adding the overhead of multiple downloads.
1. We use some internal stuff and a little bit from http://csstidy.sourceforge.net/
2. I don't have as much data on this as I'd like in order to say definitely yes, but my initial testing has shown it to improve. Hoping to look at this more soon.
3. No, it doesn't yet, but we are planning to add this soon.
5. We set the visibility of the body to hidden until the CSS is applied to the document in order to prevent FOUC. I didn't mention this in the post, so thanks for bringing it up.
I don't have any stats on the localStorage size vs cache sizes handy, but we'll probably address those in a future post when we have some more data on how these optimizations are performing in the wild.