The one I want to point out the most is WebScrapbook, which is alternative to SingleFile. It can either snapshot the current DOM or the document source (handy for PDFs), can use proper directory structure and provides full-text search over the stored pages.

It has support for separate server should you want to keep the files outside browser storage or share an instance between several browsers. I use this with text browser as renderer to make summarizing pages into VimWiki easier.

Unfortunately it can't do sync between instances, that's something I wanted to add to it but I'm currently juggling way too many other projects.

Then there's Feed Previews for getting those RSS/ATOM feeds where they still exist so I can avoid using the browser, or worse, getting notifications through antisocial media. (-:

Web Archives is making access to webpage archives much more convenient. Especially useful when dredging through old academic research pages full of link rot, or using TOR and getting locked out constantly.

For managing tabs I'm sticking with the venerable Tree Style Tabs together with few handy plugins like TST: Colored Tabs and TST: Unload Tabs.

While I prefer keyboard control for most things, and certainly Tridactyl goes the furthest from existing addons, it just can't really handle all the screens as it was possible with the XPI addons. sheds a tear

For content blocking it's the run of the mill uBlock with JS disabled by default (F8 mapped to selectively enable it on a page) and LocalCDN which has rule generator for whitelisting locally provided resources in uBlock.

And because some sites are broken mess and don't work even with conservative Firefox setup I've had to use Allow CORS once or twice.

Non-addon bonus: Searx-NG has a CSV output which can be integrated with tools like rofi or dmenu so you can do web searches outside web browser and easily pick the result.