Device fingerprinting can be very difficult to defend against. As you note, fonts and plug-ins can leak a lot of system entropy. The best defense against that is to disable Flash and Java, and use a common set of plugins. JavaScript can be used to obtain a lot of information about your browser and your computing environment. Your User Agent and any number of system configuration (rare or multiple screen configs, for example) can also leak a lot of entropy.
If fonts are your main concern, it may be best to browse using a cleanly-installed system or Virtual Machine.
Other potential (partial) solutions:
Tor [https://www.torproject.org/] - when used carefully, can give you a high degree of anonymity.
Disable Flash and Java to minimize font leakage.
Control JavaScript carefully, for example using the NoScript add-on [http://noscript.net/]. Be aware that this is quite a high-maintenance process.
Use Firefox extensions such as FireGloves [http://fingerprint.pet-portal.eu/?menu=6] to alter the User Agent your browser presents.
And don't forget about all of the other basics such as IP address (use Tor, VPN, SSH tunnel, or other proxy), cookies and other saved state (clean your browser of these frequently), and the sheer numbers of trackers that follow you as you browse (consider strong tracker blocking via hosts file, browser plugins, DNS, and/or proxy).