Rated 5 out of 5 stars

5 stars for the extension... except in FF57 in wich it's not working anymore.
As mentioned here (see below posts from WakeUp and from Anonymous 4 days ago), I had to use Autohotkey to get a kind of solution. However I had to replace the Tab key by the Page Up/Down keys.
(I'm using it with the excelent "Tree Style Tabs" extension, for vertical tabs)
Here it is :

#IfWinActive ahk_class MozillaWindowClass
;MouseGetPos, [OutputVarX, OutputVarY, OutputVarWin, OutputVarControl, 1|2|3]
~WheelDown::
MouseGetPos X, Y
if ( X < 205 )
SendInput ^{PgDn}
Return
~WheelUp::
MouseGetPos X, Y
if ( X < 205 )
SendInput ^{PgUp}
Return