I installed it but I am clueless on how to use it. If someone can give a short explanation on how to actually use this extension then that would be marvelous!
That's not a correct interpretation of the permission:
Access your data for sites in the “named” domain
The extension could read the content of web pages you visit in the specified domain, as well as data you enter into those web pages, such as usernames and passwords.
It requires permission to modify said domains to remove the paywall from their articles.
These extensions work first by looking at the contents of the page you're on to detect a paywall, and then make modifications to the page that remove the paywall. There's no way for the browser-creators to guarantee that the extension isn't also silently adding a hidden element that captures everything that you type into that website, in addition to the paywal removal, so they're basically trying to warn you such a thing could happen.
And that is a genuine risk from every extension in the addons store, but I would say that risk is potentially even higher with a piracy extension installed from a github relese. (Not this one in particular per se, which I have no opinion about, just in general.) If it makes you uncomfortable, a reasonable compromise could be to create a new browser profile for use only with this extension, or maybe even use a different browser entirely than your daily driver.
Maybe I'm missing something but I don't see any option to install from files with Fennec? Only from a collection. And it seems you can't add bypass paywalls clean to a collection because it's not in the AMO.
How do I install this on Firefox desktop and Firefox Android? I remember there was an extension for Firefox the last time I checked. Now I cannot find the extension on the Mozilla store.
If you are using Firefox just go to the github repo that someone linked above, go to "Releases" and then download the clean-latest.xpi file. Firefox will install it for you.
If using Chrome, I would guess it to be the same, but the right file would be the .crx one.
If you are not using Firefox+uBO you really should, though!
I'm on Pixel 7 and current Firefox, but it won't install. It Just says "no app found to open xpi files"
Edit: fixed. Have to engage Dev options. Settings > About > tap the Firefox icon a few times. Then go back to settings and you'll see the "install add-on from file" option.
If you are using Firefox just go to the github repo that someone linked above, go to "Releases" and then download the clean-latest.xpi file. Firefox will install it for you.
If using Chrome, I would guess it to be the same, but the right file would be the .crx one.
If you are not using Firefox+uBO you really should, though!