Within the "Storage"-tab in developer tools the indexeddb will be listed.

https://developer.mozilla.org/en-US/docs/Tools/Storage_Inspector

However, to get a look at the indexes, it's a bit different than in chromium (Chrome/Edge..) developer tools: In FF you have to select the database itself. After that you can select the object store on the right to get a more detailed view of the object store meta data.