Fixed issues with drag-and-drop functionality on Linux. (Bug 1897115)

For anyone that has to wait for their distro package manager before they get this update, here is a workaround for the most annoying bug (losing the ability to drag/re-order tabs in Firefox):

If the bug is present, you will find that drag-and-drop functionality has seized working in Firefox and it is not possible to select and drag drop images, texts, URLs, tabs etc.

4 Either restart Firefox or do the following to restore drag-and-drop functionality:

a Open another application like a text editor.

b Enter some random text, select it en drag it unto the URL-bar area in Firefox.

This will cause Firefox to try and open the selected text as if it were a URL.

c After this, try step 1 again to see if drag-and-drop functionality has returned.

• https://bugzilla.mozilla.org/show_bug.cgi?id=1897115