The move to WebExtensions (a shared standard for extensions in Chrome/Firefox/Edge/Opera/etc) is great.
It makes it much easier for extension developers (most of which work for free, on open-source projects) to maintain support for multiple browsers with a shared codebase.
UPDATE: new version of Video DownloadHelper addon for Quantum Firefox was not useful for me: it requires external companion app to write files (which I don't trust and don't want to install). But I found another addon: "Flash and Video Download", which does its job quite well without any assistance from external software.
This one surprises me the most, not the fact that DownThemAll itself isn't WebExtensions compatible, since that was known since last year [0], but that there is a huge gap in download management functionality.
I'm not even asking for all of the functionality present in DownThemAll, I'd just like:
* to be able to queue up multiple downloads without actually starting them, so I can start/resume them once I go AFK for example
* auto-scan all links on the page and be able to filter them to add links to the download queue, e.g. to queue up all files matching a certain filter
* rearrange the queue's order
* persist the queue across browser sessions
* pause any given download and be able to resume it across browser sessions
Meanwhile the usual built-in download functionality nowadays appears to be pitifully bare-bones by comparison, only providing the ability to manually download individual files one by one with no semblance of a queue, nor a way to limit concurrent downloads to one (e.g. I'd rather have one finished and ready to use than 5 downloading slowly due to the connection being spread thin).
For what it's worth, thankfully the author of DownThemAll is working on a WebExtensions version [1], which may also get released on Chrome and other WebExtensions-compatible browsers [2].
A subset is currently being rewritten. Which is a surprise because he announced he wanted nothing more to do with Mozilla over this, last year. Wonder what caused the change of heart.
From research I also found Vimium-FF and Saka Key. I just dread the whole process of trying each one out (I'll probably just settle for the first or second one I try) and subsequently re-customizing everything. It took me hours to get Vimperator where I wanted it (between the learning curve and modifying settings) and to lose that is like losing my .vimrc file.