3.5 Upgrade: Media upload, screen options and others not working

I just upgraded to 3.5 but a lot of functions are no longer working:

– media upload doesn’t open when clicking on it
– collapsing boxes no longer works
– screen options doesn’t open

I have tried the following:

– disabling all plug-ins
– updating all plug-ins
– adding a line of code that was mentioned here somewhere

The theme I am using is Wigi by Themify.me, and they posted last Friday that all their themes have been tested and are working with 3.5.

I get the following (javascript) errors on the “add new post” page:

[10:49:28.251] TypeError: f(…).on is not a function @ https://www.level30.nl/wp-includes/js/media-models.min.js?ver=3.5:1
[10:49:28.428] Use of getAttributeNode() is deprecated. Use getAttribute() instead. @ https://www.level30.nl/wp-content/themes/wigi/themify/js/jquery.js:16
[10:49:28.430] TypeError: c.on is not a function @ https://www.level30.nl/wp-admin/js/common.min.js?ver=3.5:1

[10:49:27.157] Unknown property ‘box-sizing’. Declaration dropped. @ https://www.level30.nl/wp-includes/css/admin-bar.min.css?ver=3.5:1
[10:49:27.157] Error in parsing value for ‘background-image’. Declaration dropped. @ https://www.level30.nl/wp-includes/css/admin-bar.min.css?ver=3.5:1
[10:49:27.320] Error in parsing value for ‘filter’. Declaration dropped. @ https://www.level30.nl/wp-includes/js/thickbox/thickbox.css?ver=20121105:37
[10:49:27.320] Unknown property ‘-moz-opacity’. Declaration dropped. @ https://www.level30.nl/wp-includes/js/thickbox/thickbox.css?ver=20121105:38
[10:49:27.320] Error in parsing value for ‘height’. Declaration dropped. @ https://www.level30.nl/wp-includes/js/thickbox/thickbox.css?ver=20121105:44
[10:49:27.320] Error in parsing value for ‘margin-top’. Declaration dropped. @ https://www.level30.nl/wp-includes/js/thickbox/thickbox.css?ver=20121105:65

[10:49:27.322] Error in parsing value for ‘background-image’. Declaration dropped. @ https://www.level30.nl/wp-includes/css/buttons.min.css?ver=3.5:1
[10:49:27.324] Unknown property ‘user-select’. Declaration dropped. @ https://www.level30.nl/wp-includes/css/media-views.min.css?ver=3.5:1
[10:49:27.324] Error in parsing value for ‘background-image’. Declaration dropped. @ https://www.level30.nl/wp-includes/css/media-views.min.css?ver=3.5:1
[10:49:27.330] Unknown property ‘box-sizing’. Declaration dropped. @ https://www.level30.nl/wp-admin/css/wp-admin.min.css?ver=3.5:1
[10:49:27.330] Unknown property ‘user-select’. Declaration dropped. @ https://www.level30.nl/wp-admin/css/wp-admin.min.css?ver=3.5:1
[10:49:27.330] Error in parsing value for ‘filter’. Declaration dropped. @ https://www.level30.nl/wp-admin/css/wp-admin.min.css?ver=3.5:1
[10:49:27.332] Error in parsing value for ‘background-image’. Declaration dropped. @ https://www.level30.nl/wp-admin/css/wp-admin.min.css?ver=3.5:1
[10:49:27.337] Error in parsing value for ‘background-image’. Declaration dropped. @ https://www.level30.nl/wp-admin/css/colors-fresh.min.css?ver=3.5:1
[10:49:27.362] Error in parsing value for ‘cursor’. Declaration dropped. @ https://www.level30.nl/wp-content/plugins/co-authors-plus/css/co-authors-plus.css?ver=3.0.3:37
[10:49:27.525] Expected end of value but found ‘0’. Error in parsing value for ‘background-image’. Declaration dropped. @ https://www.level30.nl/wp-includes/css/editor.min.css?ver=3.5:1
[10:49:27.525] Error in parsing value for ‘filter’. Declaration dropped. @ https://www.level30.nl/wp-includes/css/editor.min.css?ver=3.5:1
[10:49:27.526] Error in parsing value for ‘background-image’. Declaration dropped. @ https://www.level30.nl/wp-includes/css/editor.min.css?ver=3.5:1