Having a character sheet open causes slowdowns and stutters across my entire computer

They specifically said "in the next hour or so" which is pretty close to "immediately". So either the fix didn't work and needs to be reported (as Elasir5 is doing), or something went wrong implementing the fix and they haven't bothered to update anyone.  Much like the Dragonmark issue that DDB have reported as fixed twice, but is apparently still broken with no further updates from them.

From Stukov's link

That will be fixed in the next hour or so. We put a temporary fix in place a few weeks ago for that issue, thought we had a permanent fix for it so we reverted the temp fix late last week. Looks like that didn't solve it, so the temp fix is going back in momentarily.

Sadly the problem is still present in firefox version 150.0