Firefox misplaces cursor when moving between lines

When the cursor is programmatically moved, as we need to do
from time to time, Firefox's internal reference for the appropriate
cursor location on nearby lines is maintained, creating an
unexpected experience.

The fix is to wiggle the selection. This tricks Firefox into thinking
that it adjusted the selection natively.

Bug: 48289
Change-Id: I75e7e4467ec1c3faf344709886b9be5b1423cd3e
Merge "Firefox misplaces cursor when moving between lines"