"Validating the marking of an essay question attempt." fails on windows FF

"Validating the marking of an essay question attempt." scenario fails on Windows FF, as the time to check "Save changes" takes long enough and window is closed before switching.

2 ways to solve this:

1. No extra step after saving changes, to ensure the switch window works.
2. Increase timeout for the preview window,

This was discussed in MDL-51322 and thuiner had concerns about the check after saving, to ensure we don't have any debugging on that page.

I tried with increasing the timeout (2nd option) but it still fails on win-ff, so going with 1st option to make this scenario pass on all platforms.