In Firefox 3 Mozilla wanted to make dragging and dropping items in the browser a little more intuitive, and so they decided to show a preview of the item your dragging underneath the mouse cursor. On Windows and Macs the image should be translucent like the tab preview shown in the screenshot above, but on Linux the preview image is not transparent.
I’ve been wanting to disable the preview image for quite some time because it’s more difficult when trying to drag and drop things. For example, I frequently bookmark sites by dragging the tab into the bookmark sidebar, and I always drop the tab onto the folder where I want the bookmark to reside. Sometimes the preview image gets in the way, kind of like it does in the screenshot above where it’s a little difficult to see the “drop indicator.”
How can you disable this feature? Miles left a comment on one of our Firefox tips pointing to a setting that will instantly disable the preview image. To do this you need to open the about:config and find the nglayout.enable_drag_images setting. Set the value to false by double-clicking on it, and the changes will be applied without needing to restart the browser. Refer to this article if you need help using about:config.
Once the setting has been changed to false anything that you try to drag and drop will merely show a box outline instead of the preview image, and this makes it a lot easier to see where exactly you’ll be dropping the item.
A million thanks to Miles for digging up this hidden gem!