- re-use ProxifiedUrl to implement AbsoluteProxifyURL, reducing the copy-pasta
- reduce the internal indentation of ProxifiedUrl by inverting some conditions
- Reduce the amount of nested loops: it's preferable to search the whole page
once and filter on it (even with filters that should always be false),
than searching it again for every element we're looking for.
- Factorize the proxying conditions into a `shouldProxy` function to reduce the
copy-pasta.
