fixes #282 the long standing jumpy toolbar.

thx a lot to @andrey013 and the folks from mozilla.

There is a short video for Jeremy:  http://youtu.be/pxKSxKoMeRY that shows the problem. 
The file tw contains the patch already. I hope there are no side effects.

There should be a second issue somewhere, that should be fixed now. I'll have to investigate. ..