Set firefox options is not working

#### What are you trying to achieve?
Set download options in firefox similar to what we can do with chrome. See yaml below.

#### What do you get instead?
Options are empty in firefox browser when I open url about:config.

### Details
* Codeception version: 4.1.17
* PHP Version: 7.4
* Operating System: Ubuntu 20.04 inside a docker container
* Installation type: Composer
* List of installed packages (`composer show`)
```
behat/gherkin v4.8.0 Gherkin DSL parser for PHP
codeception/codeception 4.1.17 BDD-style testing framework
codeception/codeception-progress-reporter 4.0.3
codeception/lib-asserts 1.13.2 Assertion methods used by Codeception core and Asserts module
codeception/module-asserts 1.3.1 Codeception module containing various assertions
codeception/module-db 1.1.0 DB module for Codeception
codeception/module-filesystem 1.0.3 Codeception module for testing local filesystem
codeception/module-webdriver 1.2.0 WebDriver module for Codeception
codeception/phpunit-wrapper 9.0.6 PHPUnit classes used by Codeception
codeception/stub 3.7.0 Flexible Stub wrapper for PHPUnit's Mock Builder
doctrine/instantiator 1.4.0 A small, lightweight utility to instantiate objects in PHP wi...
guzzlehttp/guzzle 7.2.0 Guzzle is a PHP HTTP client library
guzzlehttp/promises 1.4.0 Guzzle promises library
guzzlehttp/psr7 1.7.0 PSR-7 message implementation that also provides common utilit...
hoa/consistency 1.17.05.02 The Hoa\Consistency library.
hoa/console 3.17.05.02 The Hoa\Console library.
hoa/event 1.17.01.13 The Hoa\Event library.
hoa/exception 1.17.01.16 The Hoa\Exception library.
hoa/file 1.17.07.11 The Hoa\File library.
hoa/iterator 2.17.01.10 The Hoa\Iterator library.
hoa/protocol 1.17.01.14 The Hoa\Protocol library.
hoa/stream 1.17.02.21 The Hoa\Stream library.
hoa/ustring 4.17.01.16 The Hoa\Ustring library.
joomla-projects/joomla-browser v4.0.0.x-dev b5afd92 joomla-browser Codeception Module
myclabs/deep-copy 1.10.2 Create deep copies (clones) of your objects
nikic/php-parser v4.10.4 A PHP parser written in PHP
phar-io/manifest 2.0.1 Component for reading phar.io manifest information from a PHP...
phar-io/version 3.0.4 Library for handling version information and constraints
php-webdriver/webdriver 1.9.0 A PHP client for Selenium WebDriver. Previously facebook/webd...
phpdocumentor/reflection-common 2.2.0 Common reflection classes used by phpdocumentor to reflect th...
phpdocumentor/reflection-docblock 5.2.2 With this component, a library can provide support for annota...
phpdocumentor/type-resolver 1.4.0 A PSR-5 based resolver of Class names, Types and Structural E...
phpspec/prophecy 1.12.2 Highly opinionated mocking framework for PHP 5.3+
phpunit/php-code-coverage 9.2.5 Library that provides collection, processing, and rendering f...
phpunit/php-file-iterator 3.0.5 FilterIterator implementation that filters files based on a l...
phpunit/php-invoker 3.1.1 Invoke callables with a timeout
phpunit/php-text-template 2.0.4 Simple template engine.
phpunit/php-timer 5.0.3 Utility class for timing
phpunit/phpunit 9.5.2 The PHP Unit Testing framework.
psr/container 1.0.0 Common Container Interface (PHP FIG PSR-11)
psr/event-dispatcher 1.0.0 Standard interfaces for event handling.
psr/http-client 1.0.1 Common interface for HTTP clients
psr/http-message 1.0.1 Common interface for HTTP messages
ralouphie/getallheaders 3.0.3 A polyfill for getallheaders.
sebastian/cli-parser 1.0.1 Library for parsing CLI options
sebastian/code-unit 1.0.8 Collection of value objects that represent the PHP code units
sebastian/code-unit-reverse-lookup 2.0.3 Looks up which function or method a line of code belongs to
sebastian/comparator 4.0.6 Provides the functionality to compare PHP values for equality
sebastian/complexity 2.0.2 Library for calculating the complexity of PHP code units
sebastian/diff 4.0.4 Diff implementation
sebastian/environment 5.1.3 Provides functionality to handle HHVM/PHP environments
sebastian/exporter 4.0.3 Provides the functionality to export PHP variables for visual...
sebastian/global-state 5.0.2 Snapshotting of global state
sebastian/lines-of-code 1.0.3 Library for counting the lines of code in PHP source code
sebastian/object-enumerator 4.0.4 Traverses array structures and object graphs to enumerate all...
sebastian/object-reflector 2.0.4 Allows reflection of object attributes, including inherited a...
sebastian/recursion-context 4.0.4 Provides functionality to recursively process PHP variables
sebastian/resource-operations 3.0.3 Provides a list of PHP built-in functions that operate on res...
sebastian/type 2.3.1 Collection of value objects that represent the types of the P...
sebastian/version 3.0.2 Library that helps with managing the version number of Git-ho...
symfony/console v5.2.3 Eases the creation of beautiful and testable command line int...
symfony/css-selector v5.2.3 Converts CSS selectors to XPath expressions
symfony/deprecation-contracts v2.2.0 A generic function and convention to trigger deprecation notices
symfony/event-dispatcher v5.2.3 Provides tools that allow your application components to comm...
symfony/event-dispatcher-contracts v2.2.0 Generic abstractions related to dispatching event
symfony/finder v5.2.3 Finds files and directories via an intuitive fluent interface
symfony/polyfill-ctype v1.22.0 Symfony polyfill for ctype functions
symfony/polyfill-intl-grapheme v1.22.0 Symfony polyfill for intl's grapheme_* functions
symfony/polyfill-intl-normalizer v1.22.0 Symfony polyfill for intl's Normalizer class and related func...
symfony/polyfill-mbstring v1.22.0 Symfony polyfill for the Mbstring extension
symfony/polyfill-php73 v1.22.0 Symfony polyfill backporting some PHP 7.3+ features to lower ...
symfony/polyfill-php80 v1.22.0 Symfony polyfill backporting some PHP 8.0+ features to lower ...
symfony/process v5.2.3 Executes commands in sub-processes
symfony/service-contracts v2.2.0 Generic abstractions related to writing services
symfony/string v5.2.3 Provides an object-oriented API to strings and deals with byt...
symfony/yaml v5.2.3 Loads and dumps YAML files
theseer/tokenizer 1.2.0 A small library for converting tokenized PHP source code into...
webmozart/assert 1.9.1 Assertions to validate method input/output with nice error me...
```
* Suite configuration:
```yml
class_name: AcceptanceTester
modules:
config:
WebDriver:
host: 'selenium-test'
port: 4444
url: 'http://web-test'
browser: 'firefox'
restart: true
clear_cookies: true
window_size: 1024x1024
capabilities:
unexpectedAlertBehaviour: 'accept'
'goog:chromeOptions':
prefs:
download.default_directory: "/tmp/tests"
'moz:firefoxOptions':
prefs:
browser.download.folderList: 2
browser.download.defaultFolder: "/tmp/tests"
browser.download.dir: "/tmp/tests"
browser.download.downloadDir: "/tmp/tests"
browser.download.useDownloadDir: true
browser.helperApps.neverAsk.openFile: "application/csv"
username: 'admin'
password: 'admin'
database host: 'mysql-test'
database user: 'root'
database password: 'root'
database name: 'sites'
database type: 'mysqli'
database prefix: 'j_'
error_level: "E_ALL & ~E_STRICT & ~E_DEPRECATED"
```