Nit: add a space between "profile" and the equals sign.

Also, nit: I hear plans are afoot to land this code in mozilla-central, so it's worth adopting more of its formatting conventions, even if we prefer alternatives. I'm thinking here specifically of the Mozilla convention to surround all conditional blocks with braces, even one-line one-statement blocks like these:

```
    let profile;
    if (Prefs.gaiaProfile) {
      profile = Prefs.gaiaProfile;
    } else {
      profile = URL.toFilename(PROFILE_URL);
    }
```

However, in this case you can probably reduce this logic to a single statement using the tertiary operator:

```
    let profile = Prefs.gaiaProfile ? Prefs.gaiaProfile : 
                                      URL.toFilename(PROFILE_URL);
```

Or perhaps even to a single line:

```
    let profile = Prefs.gaiaProfile || URL.toFilename(PROFILE_URL);
```