In some ways, we've taken a few steps back from a programmable web—two things I miss: bookmarklets and user scripts. Imagine having a bookmarked shortcut to do complex things like taking screenshots or saving a PDF. Or running scripts to automatically change the styling of websites, removing annoying sections (not just ads!). All of this used to be possible.
Brendan Eich, the author of JavaScript, thought that we'd use JavaScript bookmarklets to run arbitrary scripts against the DOM:
They were
What happened to bookmarklets and user scripts? I must have missed the boat because I’m still using them.
I keep all of my user scripts at https://userscripts.kevincox.ca/ and use a few made by others.
I only have one bookmarklet, it generates email addresses for me and injects them into a form. But I use it frequently.
I do agree that most people have moved to browser extensions. It is a shame that browsers didn’t just integrate and improve user scripts. You could imagine that WebExtensions could have just been extra APIs instead of a big browser-integrated thing with a mandatory app store. I think this is a common problem that we keep running into, centralized stores rather than decentralized installation methods.