I came across this @ mozilla.dev.apps.firefox related to 64-bit Firefox development:
I've rarely opened more than twenty tabs and am wondering what sort of usage would require that "users often have hundreds or even thousands of tabs".After I announced my decision to disable 64-bit Windows nightlies, there
was significant negative feedback. After reviewing that feedback, and
consulting with Release Engineering, I believe that we can keep a set of
users happy by making a modification to the original plan.
Most importantly, it seems that there are users who regularly run into
the 4GB memory limits of 32-bit builds. These users often have hundreds
or even thousands of tabs. These users are using the 64-bit nightlies
not primarily to be part of our testing community, but because those
builds are the best product available.