What version are you running?
2.0.11
What's the URL of the page containing the problem?
/r/5151/diff/
What steps will reproduce the problem?

Create a review with a completely new file being added
Left-click on the green diff of the new file to drag and select its contents

What is the expected output? What do you see instead?
Expected: Code should be selected, to allow copy & paste

Actual: Nothing happens
What operating system are you using? What browser?
Mac OSX 10.11.6

Chrome 63.0.3239.132

Firefox 58.0.1

Safari 11.0.3 (11604.5.6.1.1)
Please provide any additional information below.

I can select code for files with changes (two columns, with yellow background)
I can "sort of" select code for new files by clicking and dragging in the left margin (the white border to the left of the line numbers), and then the whole file gets selected up to that point.
But if I left-click and drag on the code of a new file, nothing happens.
Right-click works as expected, displaying the right-click menu