Source list does not appear in Internet Exploder

Looking in the IE11 dev console, I find two errors that hint at the underlying problem, one about a missing `fill` property and one about a missing `startsWith` property (or maybe it was `endsWith`). More issues might turn up if we solve these.

When the frontend code is more stable (i.e., not yet), experiment with fixing IE11 support. Keep an eye on the time; if it is very time-consuming, we might want to reconsider whether we want to support IE at all.