Currently broken on instagram.com. Until then it is one hell of great addon and helps a lot. But now it's useless for me.

This could be a 5 star extension, it is the best available for what it does. I do however wish I could manipulate more than 1 variable for the regex captures, for example to combine part of the :pagetitle: and part of the :pageurl: into a single filename. Currently it only works with one or the other, unless you don't customize the variable and take the whole mess to create one giant filename. Alternatively a regex replace option could offer the cleanup needed prior to saving. Also, if this extension could be triggered via javascript or an extension that would be amazing, would love to be able to use hotkeys to pass a resource url to Save-In... for acquisition.

It won't save images with direct urls that don't end in the format type, such as ones from Twitter. Example:
https://pbs.twimg.com/media/D8QhvV_UYAAlvAw?format=jpg&name=orig

Options in preferences disappear in Firefox 67 and hotkeys stop work. But plugin so good!

need a savelink extension functionality, since that one is dead (save url of the page as an .url file in a predefined directory with predefined filename pattern, with a single button click)

For saving out of the default (on Windows) you can use application called "Link Shell Extension" a graphical mklink install then on the target directory right click & chose "pick link source" then right click on default directory & chose "Drop As.." & chose symbolic link or Junction then you will have the target directory in the default directory & the directory name to "Save in" setting.
http://schinagl.priv.at/nt/hardlinkshellext/linkshellextension.html
You need Administrator right

I have a lot of links like "download.php&id=1234". This extension saves all those links as file with "download.php" name. While FF itself honors Content-Disposition response header (filename parameter).