Gandalf
hehehe
to each their own ^^
it's just the main features that made me use firefox are going away. so yep it will be pretty much dead for me.
Panorama was actually a feature of firefox, a great feature I might add but completely ignored by the general public, and it stayed half-baked lacking a lot of features that were actually needed for it to work correctly.
example: how many friends of me complained about losing their session ? a lot
yes there's backups in firefox, however it doesn't always allow recovering.
example : once I had some crash in firefox, can't recall why, however while trying out stuff to stop it crashing, I restarted the browser about a dozen times, with default firefox in this case, all your sessions are overwritten by empty ones at this point.
So, end of line, when you have an unreliable session keeping, who's gonna bother with setting up tab groups ?
Same story with the addon, Multiple Tab Handler, which is pretty much a requirement if you're gonna use tab groups.
Without it, using tab groups is a tedious process of doing everything 1 by 1.
Then it got segregated as an addon, however with this actually came finally some updates of that feature.
And now it's gonna die with firefox 57
And for your knowledge, multi-XPI disappearance was silently dropped so "announced years ago" seems a bit over the top.
As for moving forward with webextensions, I'll direct you to tabs groups author post, he knows much more than I do on the subject: http://fasezero.com/addons/
from reading his stuff it seems to me that it's not that black & white as you seem to imply.