Graphical error with drop shadow in Firefox and Thunderbird. Any suggestions?

[allan_zip]

I am seeing some intermittent but unusual graphical errors in the rendering of my window drop shadows when using Thunderbird 6 and Firefox 5.01.
It is apparent if I open a Finder window over either of the apps and also if I open, for example, the download window in Firefox itself. Difficult to describe the nature of the error, it is as if the background window stays 'greyed out' and the overlaying window erases that grey with it's drop shadow. I have attached an example below, an xPad window over Firefox:

You can see where the overlaying window has 'erased' the background shadow.
I have posted at the Mozilla support forums but have received no response.
Does antyone have any ideas how to fix or troubleshoot this. Is there a possibility it could be a problem with Snow Leopard? I'm on a MacBook Pro 8,1 running 10.6.8
Thanks for any help.
Al

 

[allan_zip]

Have updated Firefox to 6 also and not seeing any improvement there.

 

[psxguru]

It does this on my MBA with Lion

 

[allan_zip]

I'm seeing it predominantly when Firefox and Thunderbird are open, is this similar to your own experience?

 

[psxguru]

Yes with FF (I don't use Thunderbird), when I switch focus to another overlapping window it will usually manifest itself. Seems like some screen redraw event isn't being handled correctly.

Sometimes it will correct itself in the background if I've left FF on gmail as the Ajax mail check event causes a redraw (or more usually a flicker in the background)

 

[allan_zip]

Yep, that's the very same as me.