Gmail was one of the first applications making use of it, but there are many other applications like Talkwheel using it. These applications are able to detect when the user is running chrome and they offer a link to the user to enable the feature.
A last problem, is that chromeframe has a bug which prevents to show the info bar to authorise websites to use notifications, so you have to follow these steps to enable notifications in IE:
- Open IE and Install chromeframe from this URL, if you did not it before.
- Add the entry below to your windows registry. You can do either, import the key by clicking over this link, or run 'regedit' and add the entry by hand as is shown in the screenshot below.
- Now you can open the chrome settings page just typing: gcf:chrome://settings/content in the url box.
- Finally you have to enable notifications.
It seems that FireFox will support 'Desktop notifications' soon, since it is part of the html5 specification, in the meanwhile you can install the ff-html5notification plugin by clicking on this link.