<link href> URLs not rewritten
Another kind of URL that doesn't get rewritten is one mentioned in a tag.
(This is kind of similar to the prefetch issue because prefetches are indicated with tags too.)
An example, from https://twitter.com/twittersearch, is
Even if a rule affects those URLs, they don't get rewritten, and they appear to create a mixed content warning. I'm not sure whether they get loaded, or simply ignored (I haven't checked with Wireshark).
To upload designs, you'll need to enable LFS and have admin enable hashed storage. More information