This is a followup on 312c72c364, which did the same on the main code base,
and is preliminary work for tidying up John's changes in the following commits.
No functional changes.
Command:
find tests/frontend -name '*.js' -type f -print0 | xargs -0 sed --in-place 's/[[:space:]]*$//'
These changes make the frontend tests send keydown instead of keypress in
firefox, in accordance with #3413 (Use keydown instead of keypress on Firefox).
The percentage of passing frontend in Firefox 61 on this revision is 100%.
