When I go back to view a difficult card, which I have just answered correctly, I like to replay the audio multiple times and speak along because it helps me remember the words (currently I'm tapping left arrow to get back to the card and then right arrow followed by the left arrow to do this--which isn't ideal because it forces me to refocus on the text which has just reappeared and, rarely, causes me to accidentally tap right arrow on my new card).
For sentences that I find particularly difficult I also copy the sentence to google translate and have the sentence spoken there as well. I am inclined to do this because google translate will slow down the text-to-speech audio on the second replay which is helpful when I'm trying to speak along with the sentence.
Ideally, I wouldn't need to use google translate for this purpose, so what I propose is that when you go back to the card that there be a hotkey (perhaps the down arrow) that replays the audio and another (perhaps shift-down arrow) that replays the audio at a slower speed.
These features would mean that I wouldn't need to switch tabs and that I would be able to Lingvist using only the keyboard (this makes me irrationally happy)!