http://www.browserleaks.com/javascript This site can detect you screen resolution, even if change you window size of JondoBrowser, while Tor Browser is not effected by this. You can do this also by shortcut key Ctrl++/-, but its not a good idea, if the website pop out a new tab, then this new tab with the normal size of the webpage. I do this because I always visit some specific sites with Tor Browser or Firefox if leak my fingerprinting the site may recognize me. Any security tips about always visit some specific sites?
The best approach is to have a separate VM for each persona. That way, no matter what the browser leaks, different personas won't have the same fingerprint. They'll stay unassociated even if one of the VMs gets hosed. Using different Linux or BSD flavors for variety, VMs share only VirtualBox features, plus what gets exposed from the host hardware. To hide information about the CPU, don't use PAE/NX.
Regarding http://www.browserleaks.com/javascript, the results I'm seeing make no sense. Anyone else seeing completely wrong information displayed under "Internet Explorer Features"?