This would need to be *user_pref* (with an underscore rather than a dash).

Also, nit: append a newline to the file.

However, this change doesn't actually suppress that dialog, which appears when you run a version of B2G with a profile that was previously used with a different version of B2G (f.e. B2G 18 and then 24.0a1 or vice-versa). To suppress the dialog, you must set the *extensions.showMismatchUI* preference:

```
user_pref("extensions.showMismatchUI", false);
```

But suppressing the dialog doesn't actually solve the problem of a broken profile. When I set the aforementioned pref in a Gaia profile, start the Simulator's build of B2G 18 with the profile, and then start a custom build of B2G 24.0a1 with the profile, the app starts, but its window never appears, and only the following messages appear in the console:

```
desktop-helper: +++ loading scripts for app: resource://gre-resources/hiddenWindow.html

AlarmHalService: Constructor
```

Going from 24.0a1 to 18 also fails, although differently. It displays the window, but the window remains black, and the following messages appear in the console:

```
desktop-helper: +++ loading scripts for app: resource://gre-resources/hiddenWindow.html

Cannot open Settings DB. Trying to open an old version?
 -*- Shell.js: patch RemoteDebugger.start
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
SettingsService failed to open DB!
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
Cannot open Settings DB. Trying to open an old version?
```