`setPreference` doesn't escape quotes in values

[ROpdebee]

Example

const profile = new FirefoxProfile();
profile.setPreference('foo', '"bar"');
profile.updatePreferences();
console.log(await readFile(profile.userPrefs, { encoding: 'utf8' }));

This leads to a file containing the following line:

user_pref("foo", ""bar"");

and FF errors out because it's invalid.

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Workaround

profile.defaultPreferences['foo'] = JSON.stringify('"bar"');
profile.updatePreferences();

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Potential fix

Use JSON.stringify in setPreference. That might be able to replace the custom cleaning logic altogether.