Serialization broken in Firefox when options are filtered

[alexanderheckel]

Browser / OS details

Firefox Version: 82.0.3
OS Version: macOS 10.15.7

Steps to reproduce the issue

1. Clone repository
2. Open demo/index.html in Firefox
3. Filter 'Option 1', select 'Option 1'
4. Run "$('#demoform').serialize()" in Console

$('#demoform').serialize()
"duallistbox_demo1%5B%5D_helper2=option1&duallistbox_demo1%5B%5D=option1&duallistbox_demo1%5B%5D=option3&duallistbox_demo1%5B%5D=option6"

Note duallistbox_demo1%5B%5D_helper2=option1&, which should not be there.

Running the same test with Chrome or Safari:

$('#demoform').serialize()
"duallistbox_demo1%5B%5D=option1&duallistbox_demo1%5B%5D=option3&duallistbox_demo1%5B%5D=option6"

Any suggestions?

[alexanderheckel]

Seems to be related to #109, which is more a workaround than a fix. Feel free to close the issue if you think this is not a bug - thanks.