Thus spake Jamie Nguyen (j@jamielinux.com):

I noticed in alpha Linux bundle (2.4.9-alpha-1) that the prefs.js still sets the user-agent as Firefox 10 instead of Firefox 17. I'm not sure which is likely to provide more anonymity, but I just wanted to check whether this was intentional or a slight oversight.

Thanks for this. I updated Torbutton's useragent spoof value and forgot about TBB's prefs.js. I just pushed an update to torbrowser.git origin/maint-2.4 and master.