I use Mozilla Firefox, and lately I have been using LingQ in a slightly reduced window (so that I can have Google chat open at the same time). LingQ displays fine in a full-size window, but a lot of things (like the tabs, and the language selector at the top of every page) don’t display or function properly in a smaller window.
We know there are some issues but you do have to go quite small to encounter them. We are hoping they will be fixed in our upcoming release.