Hopefully by now you've read about the kiddie porn site that was recently pwned by the FBI. Just like they did with Lolita City, the FBI used javascript to exploit the Windows version of the Tor Browser Bundle in order to harvest the source IPs of those who accessed the now-defunct CP site PlayPen.
There is no reason that the FBI or another LEA couldn't implant a similar exploit the next time a DNM is pwned. This has happened twice now and pedos are only the beginning. Start protecting yourself now by taking the time to use TAILS or WHONIX or some other gnu-based anonymous/amnesiac operating system for accessing the DNMs. Using the Tor Browser Bundle is Windows has become far too dangerous to risk losing your freedom over. TAILS is easier than ever to use - you can even boot from USB on a Mac now that they've switched to EFI, or just run it in a VM. I'm not a huge fan of WHONIX for other reasons, but it provides even better protection against an exploit revealing your clearnet IP than TAILS does.
Whatever choice you make, do yourself a favor and get off of Windows or risk becoming the low hanging fruit.
running TAILs in a VM does next to nothing for you.