adblockplus/adblockpluschrome ? reverse-engineered prompt

I want you to get this old Adblock Plus browser extension project working locally and give me a clean development setup I can actually use. It should build an unpacked version I can load into Chrome and Firefox for testing, and also be able to make the normal packaged build output for each browser. Please handle whatever setup the repo needs, including submodules and install steps, then run the tests and linting so we know it is in a good state.

If anything is broken because the project is deprecated, fix only what is needed to get it building and running again without changing what the extension is supposed to do. At the end, leave me with the exact commands to rebuild it, where to find the generated files, and short notes on how to load the extension in the browser. You can check current docs online if you need to.