Greasy Fork is available in English.
Moves the controls under the video and makes the UI look like it was before august 2015
The bright background is normal, but the dialog was pushed off-screen for some reason. I've narrowed the problem down to a certain css rule that was supposed to move the content under the video 35px down (to make room for the controls). Moving it down with a transform seems to conflict with how the dialog shows up...
Luckily I've found an alternative way to move the content down a while ago (but didn't include it, because it didn't seem necessary), which fixed it (v1.12.0).
Reporting dialog glitch
When clicking to report a comment, a bright background would just appear across the whole page making it impossible to get out of.
I don't know about other dialogs causing this, as this is the only one I have found so far...