Btw - the link above is to the 1.17 version. In the current 1.18.3 version the progress example doesn't work in HTML5 because of the usage of the '%$random%' url placeholder. This is a bug only in 1.18.3 and will be fixed soon in 1.18.4 and the next 1.19 releases.
The %$random% was only used to force a full reloading for testing the progress animations. When removing it, the example will work.