Thanks very much @Mark_S !
This potentially worked in Firefox, but I couldn’t get the .zip extension to work correctly for Chrome. As I am a tinkerer more than a tech expert, here’s what I did, with a new user profile (so as not to affect usual timimi installation):
First, I downloaded the .sh file, and installed it via terminal with these commands (in Terminal):
-
cd Downloads
+ enter (this is where I downloaded your revised .sh file to);
-
chmod u+x timimi-mac-arm64-250606a.sh
+ enter; and
-
./timimi-mac-arm64-250606a.sh
+ enter.
This resulted in a nice Installation successful
message: hooray!
Then I downloaded an empty.html
file from https://tiddlywiki.com/ However, on loading empty.html
into Firefox, changing the TW title, and saving, at first it simply saved in the usual “download only” way – appending (1) after empty, so there were now two files in my Downloads folder (empty.html
and empty(1).html
).
As I could see no replacement Timimi extension for Firefox in the files you kindly shared (the .sh
file seemed for the “Timimi backend” from @Riz 's excellent Timimi installation page here), I decided to install Timimi via its Firefox add-on page here. Then, saving worked in the usual Timimi way. I tried back-ups to the Downloads folder, and that worked as expected too. If I didn’t ruin the experiment by installing the usual Timimi add-on as well as your revised “back-end”, @Mark_S , then thank you very much indeed – it works great!
I tried to sideload the Chrome extension (by unzipping it, then going to Chrome extensions, enabling developer mode, and then clicking “Load unpacked”, and running the extension). However, while the Timimi fish icon appeared as an extension, I think this revised Chrome extension may need some amending: when I loaded empty.html
into Chrome and made changes, then saved, the “File saved” message appeared, but no saving happened – and on reload /refresh (cmd + R on macOS), only the original, standard empty.html
file was loaded, with all changes having disappeared.
I hope this information helps! I will be travelling for the next two or three days, and visiting family, but I will aim to log in to TalkTW in a few days time to check in, and see if there is anything else I can do to help, or if you need further information.
All best wishes, and thanks very much again @Mark_S for these efforts: if I did the Firefox update correctly, then that at least works as expected, and is perhaps already a “victory”! 
Simon