It ignores all NSFW communities. I'm planning on adding a switch for that, but if you really want, you can change nsfwFilter property in local storage through devtools. all is for everything, none is for no NSFW and only is for only NSFW communities.
Sometimes it fails to follow a community. Maybe it's because community is not yet "synced" to the instance you logged in from. Don't know much about exact reason, because I'm new to lemmy from the tech side.
There is also a planned feature to exclude whole instances. Currently only possible with editing local storage.
The code is open source, the build process is open on GitHub actions and it's hosted on GitHub pages so you also see compiled site easily. The password never leaves your browser apart from going to the instance you chose when logging in. The password also is not saved, only the access token.
I tried my best at making it as transparent as possible.
Thanks, can now log in!
Which brings me to the next problem - if I hit "follow" I just get a "community not found" error. Can you trigger a search for the community if it isn't found?