This extension is excellent although no longer being supported. I have split a single tab into 3, divided viewports. Perhaps you can do more? I did end up having to use the also-fine Stylish addon in order to override the dark background color this addon uses on pages which lack their own background color style. So thank goodness for that one as well.

Cool add-on, but...
Other extensions for the project don't work.
After arranging tabs side by side, you have to restart/re-enable uBlock, then it works on the merged tabs, but others don't (e.g., Don't care about cookies).
It would also be useful to have tab scrolling synchronization, similar to Tile Tabs WE.

I like it. I miss so badly this configuration from Zen Browser in vanilla firefox.

This addon can add several tabs into one. Mosaic view sucks, but the Iframes is quite cool. I will give 5 stars when other addons work in the Iframe view, not just for adblock, but for password manager, mouse gestures, etc