Bugzilla

When running reader mode mochitests, we log:

```
Console message: [JavaScript Error: "Not a string"]
```

It turns out (pernosco is so useful sometimes... needed a recording for bug 1659193 and decided to get to the bottom of this while there, though I don't think it's directly related) that this is a result of the telemetry calls at https://searchfox.org/mozilla-central/rev/8d108a59d067ce37671090b0b1972ee8adfb7196/toolkit/components/narrate/NarrateControls.jsm#199,204 . It's possible for `language` to be `null`, and then telemetry complains that the `key` variable is not a string.

We should still log telemetry in that case, but probably for some useful key like `no-language` or whatever. Niklas/Micah: I'm adding this to bug 1748655 because it should be a pretty straightforward fix, and running the existing reader mode browser mochitests and checking the logs can be used to verify whether things worked.

(I also pinged bug 1324774 to get these errors to be more useful...)

When running reader mode mochitests, we log:

```
Console message: [JavaScript Error: "Not a string"]
```

It turns out (pernosco is so useful sometimes... needed a recording for bug 1659193 and decided to get to the bottom of this while there, though I don't think it's directly related) that this is a result of the telemetry calls at https://searchfox.org/mozilla-central/rev/8d108a59d067ce37671090b0b1972ee8adfb7196/toolkit/components/narrate/NarrateControls.jsm#199,204 . It's possible for `language` to be `null`, and then telemetry complains that the `key` variable is not a string.

We should still log telemetry in that case, but probably for some useful key like `unknown-language` or whatever. Niklas/Micah: I'm adding this to bug 1748655 because it should be a pretty straightforward fix, and running the existing reader mode browser mochitests and checking the logs can be used to verify whether things worked.

(I also pinged bug 1324774 to get these errors to be more useful...)