Just some tips and tricks in no particular order. I just added anything I could think of or was told of. Browse them and perhaps you'll find something useful.
You can click and drag to move the subtitles vertically. On mobile, you may touch and drag instead.
One pretty hidden feature is that you can paste an image in the mining editor dialog if you have it in your clipboard. Click anywhere in the dialog and Ctrl+V. On mobile, the trick also works, but because there's no physical keyboard, you'll have to be inside a text field, like the translation one, for example, and paste the image there. This should work.
So, officially there's no such button. But you can re-import as unknown all your words. Here's how you can do it:
There's no undo button, so be careful.
Why would anyone want that ? No clue, but it exists. In the past it was possible to hold shift for that. Now you can do it by triple hitting shift (shift + shift + shift). It act as a toggle, so to revert you would hit that again. There is also a settings to enforce that all the time.
Just thought it was worth mentioning to spend time exploring the settings; there's a lot of stuff, to the point there's a search bar.