Firefox indentation bug in PR diffs

Hi,

I think I’ve found a bug with PR diffs when viewing them with Firefox. The bug doesn’t appear to affect Chrome (I haven’t tried any other browsers).

I’ve created this PR which shows the problem.

At first, when switching to the “diff” view, everything looks pretty normal. But when you click the up/down arrows to expand the diff to show more context, the indentation becomes visually different.

As you can see in the screenshot above, the code on lines 19 upwards and 27 downwards are indented further inwards.

I would expect the indentation to be the same for the line 19 upwards, 20 to 26, and 27 downwards blocks.

Note that it works as expected in Chrome (i.e. the indentation of the 19 upwards, 20 to 26, and 27 downwards blocks are the same).