Open about:config to find some spyware crap:
There is a built-in module in Firefox that improves your security, but steals your privacy and anonymity. The module reports what you download to Google servers to check if the file is infected with any kind of malware.
They hardly need your ip…
But apart from this, canvas can be used as additional entropy in web-browser’s fingerprinting and used for online tracking purposes.
The technique is based on the fact that the same canvas image may be rendered differently in different computers. This happens for several reasons. At the image format level – web browsers uses different image processing engines, image export options, compression level, the final images may got different checksum even if they are pixel-identical. At the system level – operating systems have different fonts, they use different algorithms and settings for anti-aliasing and sub-pixel rendering.
This is the first live demo of the Canvas Fingerprinting. Below you can see if HTML5 Canvas is supported in your web browser and check whether this technique can keep track of you. In addition our little continuing research will show how realy unique and persistent canvas fingerprint in real life, and whether your signature in our database (we don’t collecting anything right here!).