I think I recall this some many years ago.
For me this is a non-starter screen real-estate is important for many people, losing some on the left of the screen would be the worst of both world. The window (section) that the tabs are in make the content narrower, it also leaves huge empty space in that tab column after you get past those tabs.
Even if they fixed the left tab column so it didn't scroll, that space is lost.
I can remember when this fad was in web sites, I didn't like it then either.
Well, this is a new and improved version of side tab; it doesn't scroll with the page. When collapsed (hover to open, or pin), the side tab column takes up little horizontal real estate. Horizontal real estate is inexpensive now, what with today's wide screen monitors. Rather, I prefer to reclaim the valuable vertical real estate by moving tabs from the top to the side of the screen.
According to the email I got, this is a brand new program Firefox has implemented. If side tab isn't for you, perhaps another extension will suit the bill. There will be many to test as the program proceeds.
Regards,
PS: I found that side tab removes the advertising pane in Outlook webmail (and maybe other sites) more than giving you back the horizontal space side tab takes. See WithSidetab.png.
