[tbb-bugs] #13069 [Tor Browser]: Extreme CPU usage on downloads from mega.co.nz

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#13069: Extreme CPU usage on downloads from mega.co.nz
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 Reporter:  NewEraCracker  |          Owner:  tbb-team
     Type:  defect         |         Status:  new
 Priority:  normal         |      Milestone:
Component:  Tor Browser    |        Version:  Tor: unspecified
 Keywords:                 |  Actual Points:
Parent ID:                 |         Points:
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 Hello,

 I was downloading a 500 MB file from mega.co.nz and when it reached 99% my
 CPU gone at 100% for several minutes. I checked the temperature sensors it
 was 100ºC, I quickly killed firefox.exe (Tor Browser) and CPU usage got
 down to 1% and temperatures to be more relieving 60ºC.

 Then I quickly googled regarding the so-called javascript security
 improvements, since I've read about them in the past somewhere, and saw
 this: https://lists.torproject.org/pipermail/tor-
 bugs/2013-October/048908.html

 For the record I run NoScript with default to disable all scripts and only
 allow them temporarily on trusted sites. Also I am running mega.co.nz with
 their browser extension and download speeds reach up to 1.5 MB/sec which
 is quite fast than what I was used to in TOR.

 Back the subject, I've retried after enabling those settings manually:
  javascript.options.ion.content
  javascript.options.baselinejit.content
  javascript.options.asmjs
  javascript.options.typeinference

 And download went much better and hit 100% in the expected time with max
 15% CPU usage.

 I think there should some sort of warning about this issue somewhere. If I
 wasn't around, I'd expect having my CPU/Motherboard burnt out.

 Software versions:
 Microsoft Windows 7
 Mozilla Firefox ESR 24.8.0
 Tor Browser Bundle 4.0-alpha2
 MEGA 2.0.179

 Regards,
 NewEraCracker

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13069>
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