Export an OpenTTD Online save

First save inside the game with the floppy-disk menu → Save game.
The short silent recording starts after that save exists.

0:00–0:03 Open the host’s tools menu in the upper-left corner.
0:03–0:06 Choose Export Save. If several saves exist, select the one you want.
0:06–0:09 Choose Export to download a .sav backup.

To restore a backup, use the same host’s tools menu → Import Save, then
choose your .sav file. After the import confirmation, use the game’s
Load Game menu to open it. Importing a file does not itself load the map.
Keep a separate backup before importing a file with the same name.

OpenTTD Online: https://openttdonline.com/play/
The recording demonstrates a disposable generated map using OpenGFX2 Classic.
Credits and media source: credits.txt