As per title. Firmware available on French Hisense site, as noted on Avforums thread [https://www.avforums.com/threads/hisense-55-m3300.2028817/page-23
Works on UK tvs. Menus remain in English.
Translation of french pdf:-
Procedure for updating the 50M3300
1. Identify the correct firmware version by checking the HSSO code on the label
the back of your TV
2. If your code is well-HSSO 503300640EU, download files under:http://www.hisense.fr/telechargement/TV/K3300/50M3300/HSSO-
503300640EU / upgrade_loader.pkg (G0901 Version)
3. Put the file to the root of a USB drive formatted as FAT32
4. Connect the USB drive to the TV is on the USB2.0 port (white)
5. Record the currently installed firmware version Menu> All> About> Information
6. Turn off the TV with the remote control
7. Turn on the TV with the remote control and hold up
appearance of the message "Updating Software"
8. The Hisense logo is displayed and the update message appears
9. Wait about 10 minutes until the update is done. DO NOT TURN OFF OR UNPLUG
10. At the end of the update the TV automatically restarts
11. You can check the update in Menu> All> About> System Information
Ordered Xbox One S on the back of this..