Issue Report: store video playback very slow. Huge CPU load.

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Although playback is just fine on the latest Chrome and Firefox.
MainThrd goes up to 110% and all i get is not even 1 FPS.
Never had issues with them on Windows 7 x86 too (i dual boot).
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Using Linux Mint 13 MATE x86
Specs: http://pastebin.com/MGxm75UK

[e633]

Same videos viewed via browser (Firefox, Chrome) play just fine.
Edit: stopped a TF2 vid in steam and now navigation is impossible.
Library is ok but i'm not able to browse the store or the news or whatever.
Edit2: happened after messing with the "copy URL" and "View page source" buttons. It looks like the whole browser part of steam freezes while the page source file is open.
The only abnormal things in the console are:
--------------------------
(steam:8085): Gtk-CRITICAL **: IA__gtk_widget_get_visible: assertion `GTK_IS_WIDGET (widget)' failed
(steam:8085): Gtk-CRITICAL **: IA__gtk_widget_set_visible: assertion `GTK_IS_WIDGET (widget)' failed
(steam:8085): Gtk-CRITICAL **: IA__gtk_widget_set_visible: assertion `GTK_IS_WIDGET (widget)' failed
(steam:8085): GLib-GObject-WARNING **: invalid uninstantiatable type `<invalid>' in cast to `GObject'
(steam:8085): GLib-GObject-CRITICAL **: g_object_unref: assertion `G_IS_OBJECT (object)' failed
--------------------------
Installing breakpad exception handler for appid(steam)/version(1354925460_client)
(steam:8085): Gdk-WARNING **: XID collision, trouble ahead
Installing breakpad exception handler for appid(steam)/version(1354925460_client)
(steam:8085): Gdk-WARNING **: XID collision, trouble ahead
(steam:8085): Gdk-WARNING **: XID collision, trouble ahead
(steam:8085): Gdk-WARNING **: XID collision, trouble ahead

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Up!!!