1.9.6.8 seems to have broken StumbleUpon button

[ed]

StumbleUpon toolbar button now opens multiple tabs, some with repeats , some new stumbles.
Reported by several users and experienced by myself.

[JhnHrnndz]

I'm having the same problem and I too have seemingly narrowed it down to NoScript being the culprit. It seems like NoScript is causing StumbleUpon to open the websites it prefetches for stumbles in new tabs. Hence, the repeated websites. I've disabled prefetching and the problem seems to go away. It's also fixed when I disable NoScript in the add-on menu. Any clue as to what's going on?

[Giorgio Maone]

Looks like the code they use to prefetch is quite hackish (they create invisible browsers and load the whole document there, javascript frames and all) and gets confused by ABE when DNS records are not cached yet (i.e. almost always, since you're "stumbling" on unknown sites by definition).
I'm investigating on how to work around, either in NoScript or in SU.
In the meanwhile, you may want to disable StumbleUpon's prefetch, or NoScript's ABE (from NoScript Options|Advanced|ABE - but not very advisable, e.g. given this )

[JhnHrnndz]

I shut prefetching off because SU works fine without it. It always did seem very amateur for such a popular extension. Thanks for the quick reply.

[Giorgio Maone]

I'm working on it.
As a temporary work-around, please open StumbleUpon's Tools|Toolbar Options|Configuration and uncheck "Prefetch stumbles"

Background info here