LibRedirect

It's not particularly good at selecting instances.

Privacy frontends do not add any privacy in general compared to using the official websites and you're trusting the instance maintainer who may or may not malicious. My recommendation would be to stick with the official websites and apps unless your threat model calls for disabling JavaScript or not logging into services.

Even then, accessing these frontends can be done without an extensions as you can manually type in the url of the instance you wish to use. A browser extension has privileged access in your browser and requires you to trust the developers (LibRedirect developers in this case). Using extensions also makes you stand out thus worsening privacy and weakens site isolation, which is necessary for safe browsing.

That said, LibRedirect does have some useful features like randomly switching instances, but this does not make up for the fact you're trusting a privileged extension and reducing security and possibly privacy.

Also, LibRedirect isn't recommended by Mozilla, so it's not a trusted extension and I would never use this.

Free and open source extension which redirects links from a number of services to privacy-friendly front-ends. Supports instance switching from the extension menu, toggling instances on and off, and adding your own instances. It is the best available extension for this purpose.

Easily Redirects Invasive Social Networks to privacy-friendly frontends.

Updated: Now the extensions works flawlessly, now it is rare to get offline instances, and the extension stopped throwing you directly into the original website.

OUTDATED: Cool concept, but sadly this extension does not work most of the time, most front-end alternatives are offline, and sometimes the extension does not even try to redirect you to other frontend it just lets you enter the website directly. I really wish that this extension gets fixed, the concept is really good, but the execution is not good.