Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:2.0b10pre) Gecko/20110125 Firefox/4.0b10pre In the past two or three nightlies I started to notice that typing in the twitter "What's happening?" field has become extremely slow.

Bug 579488 is the Windows equivalent of this bug. Maybe we need to change the OS to all in that bug?

We did somethings to make this faster, see bug 579488. After that it was still not super fast. But recently Twitter has made a change to their site to make it faster. I'm going to make bug 629278 be about fixing the core issue behind the slowness.

tn, is this a dup of bug 629278?

Sure. If not, repoen.