How do I open a .c3proj project?

I'm new to Construct 3 and am trying to open a Construct 3 project someone has on their Github account. It has a project.c3proj in the root. When I try to open that in Firefox, I get the error message

A .c3proj file is part of a folder-based project and it cannot be opened this way. It must be opened using the 'Open local project folder' option instead.

I cannot find an "open local project folder" option anywhere. It is not available from the main menu?

When I try to open in Chrome, I don't even get that message - it simply does not have .c3proj as one of the file types it can open.

From other posts I've read, I'm guessing this is an older project type that Construct 3 no longer supports. If that's the case is there any way I can import what exists from this project into a new one? My repo probably has 100 or so files for various game assets in a bunch of directories.

Is there a way I could get an older version of the Constuct 3 browser that does support .c3proj files so I can open this and maybe save it in a more modern format? The .c3proj file has it's release noted as

"savedWithRelease": 37900,

Chrome supports using 'Open local project folder'. It's under Menu > Project > Open local project folder. Then you need to select the folder the .c3proj file is in. The folder needs to have the complete project in it, so if you've done something like download a zip, you need to fully extract all the files first.

Firefox does not support the 'Open local project folder' option - unfortunately they don't support the File System Access API that this feature depends on. You have to use a Chromium-based browser for that at the moment (typically Chrome or Edge).