There are a couple browser extensions that I am interested in, and I wonder if such extensions exist. But first, I have two hard requirements:

1. The extensions must be Free (libre) Software by the Free Software Foundation's definition.
2. The extension must not contain anti-features like violations of privacy.

Anyway, here are the extensions I would like:

1. An extension to block paywalled websites. In particular, this extension should work even when the paywall is porus and the site would otherwise allow the access (like nytimes, for example).

2. An extension to allow blocking of specific tweets in twitter. This extension should not require a twitter account, and the block should be specific to the individual tweet, not the username, hashtag, keywords or anything else. (This is mainly to block pinned tweets I don't like seeing all the time, or when the website/browser combination misbehaves and plays audio when I visit a user's twitter page.)

Edit: I thought of another one:

3. An extension that prevents videos from auto-playing. I would like this to be unconditional (and not, say, restricted to ads). Further, I want to still be able to get such videos to start playing manually. (In particular, this needs to work on Youtube.)

I think One could be worked into a Ublock Origin filter.

As for Two, I don't twit.

I was expecting a request for an extension to rewrite anything gender specific on a page to something gender neutral.

No, though I wouldn't be surprised if such an extension exists, and if it occasionally yields strange results.

By the way, I just edited my original post to add a third extension to my wishlist.

YouTube High Definition might interest you.  This extension lets you change the default video quality / size, auto-stop and auto-mute videos, turn off annotations and adjust the default volume.

   ▪  Firefox
   ▪  Chrome

Flash Control

Does this work for videos that don't use flash? (I intentionally do not have flash installed on this machine.)

Also, is there an equivalent for Chromium?

He doesn't want to hide/show videos, but only prevent them from autoplaying.   <span class="bold">YouTube High Definition</span> lets you do that for Youtube and embedded videos (independently).  You can also install <span class="bold">YouTube Flash Video Player</span> to choose between HTML and Flash video playback.  It's from the same developer.

Why you don't test it?

That's just not what people on these forums do.

8U Flash, in this day and age? Put that down before somebody gets hurt!

You may give YouTubeCenter
script a try.

oh, and works fine with Iceweasel on debian, no flash installed.
there is a quite long features list.

Why the downrating? I don't get it.

Dipshits interpret "Rate this post" to actually meaning "Rate this user".

Literacy these days...