Forwarding from https://commons.wikimedia.org/wiki/Commons:Village_pump#New_html5_player_issues .
I can confirm this with the example URL in Firefox 16.0.2.

I'm having an issue opening pages with high numbers of audio files (which is often the case with categories like https://commons.wikimedia.org/wiki/Category:Ogg_files_of_music_by_Frederic_Chopin ):

Browser window (Firefox) or tab (Chromium) becomes unresponsive for about 20—30 seconds until that page can be successfully viewed/scrolled. It seems that the loading of the player is the bottleneck. A possible solution would be to load and render the player conditionally, only when the user decides to play a media file.

Version: master
Severity: normal
URL: https://commons.wikimedia.org/wiki/Category:Ogg_files_of_music_by_Frederic_Chopin