[kubuntu] Firefox issues in select_file/save mask

Hi all, I'm experiencing an issue with Firefox after last updates. The mask that shows when you must save a file (or select a file to upload) doesn't work properly:

1) when I select a file (single click) it automatically starts dragging it or selecting multiple files at once;

2) clicking on the left part of the mask, the frame with the folders tree, doesn't work at all. This way I can only use the central frame to navigate, and it slows down things when you have work with a number of files and select different drives;

It's not a problem of the mouse, because it works fine with other software. This problem showed about a month ago. With the last updates it's still there. Is it some new feature that must be properly tuned by options panel or is it a bug coming with the latest updates?

Thank you