Update (Oct 22 13:15 UTC): Windows users that are affected by Tor Browser crashes might try to avoid this problem by opening "about:config" and setting the preference "media.directshow.enabled" to "false". This is a workaround reported to help while the investigation is still on-going.

Update (Oct 25 02:32 UTC): If you are unhappy with the new Firefox 31 UI, please check out Classic Theme Restorer.

Update (Oct 16 20:35 UTC): The meek transport still needs performance tuning before it matches other more conventional transports. Ticket numbers are now listed in the post.

The first release of the 4.0 series is available from the Tor Browser Project page and also from our distribution directory.

This release features important security updates to Firefox. Additionally, due to the POODLE attack, we have also disabled SSLv3 in this release.

The primary user-facing change since the 3.6 series is the transition to Firefox 31-ESR.

More importantly for censored users who were using 3.6, the 4.0 series also features the addition of three versions of the meek pluggable transport. In fact, we believe that both meek-amazon and meek-azure will work in China today, without the need to obtain bridge addresses. Note though that we still need to improve meek's performance to match other transports, though. so adjust your expectations accordingly. See tickets #12428, #12778, and #12857 for details.

This release also features an in-browser updater, and a completely reorganized bundle directory structure to make this updater possible. This means that simply extracting a 4.0 Tor Browser over a 3.6.6 Tor Browser will not work. Please also be aware that the security of the updater depends on the specific CA that issued the http://www.torproject.org HTTPS certificate (Digicert), and so it still must be activated manually through the Help ("?") "about browser" menu option. Very soon, we will support both strong HTTPS site-specific certificate pinning (ticket #11955) and update package signatures (ticket #13379). Until then, we do not recommend using this updater if you need stronger security and normally verify GPG signatures.

There are also a couple behavioral changes relating to NoScript since 3.6. In particular, by default it now enforces script enable/disable for all sub-elements of a page, so you only need to enable scripts once for a page to work, rather than enabling many sub-scripts. This will hopefully make it possible for more people to use the "High Security" setting in our upcoming Security Slider, which will have Javascript disabled globally via NoScript by default. While we do not recommend per-element whitelisting due to fingerprinting, users who insist on keeping this functionality may wish to check out RequestPolicy.

Note to MacOS users: We intend to deprecate 32bit OSX bundles very soon. If you are still using 32bit OSX 10.6, you soon will need to either update your OS to a later version, or begin using the Tails live operating system.

Read the rest here:

Tor Browser 4.0 is released | The Tor Blog