Moving widgets, adding tags, quick edit, adding image

All these things don’t work.

Details about what doesn’t work:
On the widgets page the cursor changes but the widgets can’t be moved. The Display Options tab on the widgets page doesn’t work most of the time, too (I know the work-around via direct access mode), as well as the Help tab.
The quick-edit link doesn’t load at all in some of the pages (the normal edit link works fine everywhere, however).
Adding images works only via right-klick->open link in new tab.

Details about my blog’s configs and what I’ve tried already
I don’t self-host the blog, it’s a regular username.wordpress.com thing.
I don’t have any plugins installed; actually, I don’t even have a plugins link in my sidebar in the admin thingymading.
I tried different browsers (Firefox initially worked, but then had same problems).
I tried emptying my cache, my java script is activated, I even fixed and updated my system. Still, sh*t don’t work.

Please help. I am getting really annoyed here.