This whole function can probably replaced by some usage of QTemporaryDir.

QProcess::processId()?

Probably the more modern (and cross-platform way to do this) is to use this instead of the RandomNumberGenerator and std::random_shuffle in initShuffledUrls() file:

auto generator = std::default_random_engine{};
generator.seed(time(0));
std::shuffle(v.begin(), v.end(), generator);

See: https://stackoverflow.com/questions/6926433/how-to-shuffle-a-stdvector

(seed() is needed so the random numbers generated by generator are not the same on consecutive runs of the program)

Note that rand() without srand() before will generate the same series of random numbers each program run (cf. https://www.geeksforgeeks.org/rand-and-srand-in-ccpp/) -- not what the Unix version here does!

There's http://doc.qt.io/qt-5/qfiledevice.html#setFileTime since Qt 5.10 -- but this is too recent... So you can probably leave it like that.