That could explain why it doesn't support multiprocessing. I disabled it because it doesn't do much. This is a list of its functionality from https://ubuntu-mate.community/t/what-are-the-ubuntu-firefox-...
* Enable searching for missing plugins from Ubuntu software catalog
* Add the following options to the Help menu
Get help on-line
Help translating Firefox
Ubuntu Release Notes
* Set homepage to Ubuntu Start Page
* Display a restart notification after upgrading Firefox
* Add ask.com to the search engines. You can uninstall this if you prefer to use a pristine Firefox install.
That could explain why it doesn't support multiprocessing. I disabled it because it doesn't do much. This is a list of its functionality from https://ubuntu-mate.community/t/what-are-the-ubuntu-firefox-...
* Enable searching for missing plugins from Ubuntu software catalog
* Add the following options to the Help menu
Get help on-line
Help translating Firefox
Ubuntu Release Notes
* Set homepage to Ubuntu Start Page
* Display a restart notification after upgrading Firefox
* Add ask.com to the search engines. You can uninstall this if you prefer to use a pristine Firefox install.