The project is currently in maintenance-only mode because it is basically finished and I have other priorities (most of the updates are about modifying the set of supported sources).

There is no officially supported way to import/export via a config file, but you could use the developer tools of the browser to directly read / modify the preferences.

To debug an extension, see the guide at https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Debugging

After opening a debugger for the extension's background page via about:debugging (see the above link), you can interact with the storage via the chrome.storage.local API, as documented at https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/storage/local

For example, to convert the storage to something that you can copy and paste in a file, run the following from the debugger's console:
chrome.storage.local.get(null, items => {
console.log( JSON.stringify(items, null, 4) );
});

You can then manually edit the configuration in the file (at your own risk), and save the changes back as follows:

chrome.storage.local.set();

For example:

chrome.storage.local.set({
"panelOffsets.youtube": {
"top": 100,
"right": 204,
"width": 275,
"maxHeight": 600
}
});