Plugin collections are now available on addons.mozilla.org

Those. Now users can create their own collection of plug-ins, a bunch of which in their opinion will optimally serve the goals.
Plugin collections are available at https://addons.mozilla.org/collections .
There are both custom sets and “editorial selection”.

You can also subscribe to the collection you are interested in, say Web Developer's Toolbox and keep track of those updates that will fall into this category. It is especially nice that new plugins can be monitored via RSS and special addon https://addons.mozilla.org/pages/collector

via mozilla blog