As of Feb 2016, these browsers support toBlob()
- Firefox 19
- Chrome 50
- IE10 as the prefixed
msToBlob()
Note this answer was originally written in 2011. Original answer/edits below.
toBlob() is really new and I would not recommend using it in a consumer app unless you can explicitly ask them to use a particular browser (or else control the environment).
toBlob() Was added on May 12th and is of limited functionality as-defined. It does not exist in the Chrome nightly, firefox nightly, nor IE9.
It is worth noting that Firefox does have a functional mozGetAsFile
There is yet to even be any discussion for adding it to Chrome.
The discussion for Firefox. They have decided to wait until the spec is more clear before they attempt an implementation.
The spec for toBlob() is very vague with a lot of internal questions still unresolved. They aren’t even sure what params to allow for typical toBlob() use yet.
Update on April 10th, 2012
toBlob still enjoys no support. It still does not exist on Chrome Canary (Nightly), Firefox Nightly, nor IE9.
If you want to watch for updates in Chrome star this:
http://code.google.com/p/chromium/issues/detail?id=67587
If you want to watch for updates in Firefox subscribe to this bug here:
https://bugzilla.mozilla.org/show_bug.cgi?id=648610
Update: As of February 21 2016 .toBlob now works in chrome 50 (currently canary)