It's tiring to read articles individually on mobiles or laptops. There's almost no good apps with simple reading lists and autoplay function. Google app has one, for instance, but it's not so practical and often crashes. Firefox has all the means to create the best reading list available and thus make the Firefox browser even more unique and useful.
Why not simply use Pocket?
Apart from the fact that Pocket doesn't really seem like a part of Firefox, it's not thought especially as a reading list with functions around a reading list (like read all and read aloud). Pocket is usually used to bookmark different things seen on the internet (like a tv show you wanna see tonight), so you can't simply click on "read me all" within Pocket. Also Pocket isn't practical to be used on mobiles, you need a separate app (that doesn't work on many phones, while Firefox browsers works very well, also on older phones like iPhone 6).
Most importantly, though, as mentioned the reading list could be a very valuable addition to the basic function of Firefox, appreciated by many users. And as there's no good competition yet, Firefox could make use of the "first-mover-advantage" by offering such a very much needed function as the first browser worldwide.
Thanks for your consideration!