difficulty adjusting vertical and horizontal panel sizes in gtk3 programs

[Ramiro Aceves <ea1abz%gmail.com@localhost>]

Hi,

I'm having some trouble with gtk3 programs like Thunderbird and GNU 
Radio. Adjusting the size of vertical or horizontal panels by 
interacting with the separation lines is quite difficult. There are no 
resizing arrows, and I have to position the mouse pointer very precisely 
over the panel boundaries. I'm not referring to the scroll bars.
Have you experienced this issue?

Thanks.