Form input fields placeholder text without opacity in Firefox

I recognizied that form input fields' placehilder text is not shown with opacity in Firefox, but in Chromium. Reason seems to be that some style directives in "ba-style.css" set opacity for "-webkit-input-placeholder" but not for "-moz-placeholder":

.ba-form-authorize-modal .ba-forms-modal input::-webkit-input-placeholder,
.ba-field-container textarea::-webkit-input-placeholder,
.ba-field-container input[type="text"]::-webkit-input-placeholder,
.ba-field-container input[type="number"]::-webkit-input-placeholder,
.ba-field-container input[type="email"]::-webkit-input-placeholder {
opacity: .5;
}

When adding below lines to the templates custom.css file, placeholder text is shown with opacity in Firefox as well:

.ba-form-authorize-modal .ba-forms-modal input::-moz-placeholder,
.ba-field-container textarea::-moz-placeholder,
.ba-field-container input[type="text"]::-moz-placeholder,
.ba-field-container input[type="number"]::-moz-placeholder,
.ba-field-container input[type="email"]::-moz-placeholder {
opacity: .5;
}

Is there a reason for them not to be in "ba-style.css"?