Custom Bitbucket hook with configuration screen does not always work in Firefox

[Charlie Misonne]

We have a soy file in our custom Bitbucket add-on.

It basically contains 3 checkboxes defining what configuration is used for the custom hook.

Checking any checkbox in firefox does not get saved.

In Internet Explorer this works just fine.
We can even view the result in Firefox. When saving there all checkboxes turn blank again.

When inspecting the request there is no json body. Somehow the checkboxes are not being translated in as boolean values as they should be.

Any ideas how to improve this? Atlassian's soy documentation is very limited

{namespace plugin.puppetvalidation}

/**
 * Layout for the options form
 *
 * @param config
 */
{template .formContents}
   {call aui.form.form}
       {param action: '' /}
       {param content}
             {call aui.form.checkboxField}
             {param legendContent: 'Validation' /}
              {param fields: [[
                  'id': 'validationEnabled',
                  'labelText': 'Enable Puppet validation',
                  'isChecked': $config['validationEnabled']
                  ]] /}
              {param descriptionText: 'The push will be rejected if validation fails.' /}
          {/call}
          {call aui.form.checkboxField}
             {param legendContent: 'Linting' /}
              {param fields: [[
                  'id': 'lintEnabled',
                  'labelText': 'Enable Puppet linting',
                  'isChecked': $config['lintEnabled']
                  ]] /}
              {param descriptionText: 'The push will be rejected if linting fails.' /}
          {/call}
          {call aui.form.checkboxField}
             {param legendContent: 'Linting' /}
              {param fields: [[
                  'id': 'yamlLintEnabled',
                  'labelText': 'Enable linting on yaml files',
                  'isChecked': $config['yamlLintEnabled']
                  ]] /}
              {param descriptionText: 'The push will be rejected if linting fails on yaml files.' /}
          {/call}
       {/param}
   {/call}
{/template}