what does "Switch to SAFE download mode" mean?
 

Does it mean slowly download?

It means that Xolox has found at least 1 corrupted file from the hosts it was trying to download from, and will now only download from a single host.

And yes this is normally slow.

To speed things up you can:

1. Delete and restart your download (keep your fingers crossed it doesn’t happen again).
2. Uncheck the ”switch to SAFE download” box (tools/preferences/downloads).
3. Uncheck the “drop and retry incorrect downloaded parts” box (tools/preferences/downloads)(most of the time a file will work anyway).

Try one, try all, see what works best for you.