112.0.2 (64-bit) Firefox and Thunar 1.8.14 on Ubuntu 20.04.6 LTS (Xubuntu) [sudo apt install firefox resuls in firefox is already the newest version (112.0.2+build1-0ubuntu0.20.04.1), same for thunar results in thunar is already the newest version (1.8.14-0ubuntu1)].
Dragging and dropping files to upload ceased to work. Tried on Gmail, iNaturalist, and Facebook. When dragging a file or a bunch of marked files from Thunar to Firefox, the files do not stick to the destination window as they used to (for past 20 years), visually it looks like this: when you drag the files to the destination window and release the touchpad or the mouse button to drop them, the file icons just quickly jump back to the source folder. Upload with "Upload" (and the like) button and "open file" dialog window works fine but this is not the preferable option when you routinely upload files from different source folders to different websites every day.
Rebooting Ubuntu / restarting Firefox without rebooting the entire system do not help. Dragging and dropping between folders in Thunar works fine.
Some search has shown that most answers to similar questions are "what do you mean?" and "works for me". Weird solutions with mouse gestures (like "drag files slowly, and not from the side of the Firefox window but from the bottom of the Firefox window" or "drag the files to Firefox window, then back, and then back to Firefox again") which seemed to work in some cases do not work either. Failed to locate any reasonable answer (like: "this is a known bug, we are fixing it", or: "launch firefox with this and that switches on", or: "go to Firefox 'settings' menu and do this and that") so far.
What I prefer not to do: (1) Upgrade to 22.04. Any other ideas (like running some command-line diagnostics) would be appreciated. Please, do not recommend just to "read the log files" without specifying which log files should be read and what is to be sought in them for I am a bear of very little brain, and long words bother me (c).
Update: Drag and drop in Firefox windows seemed to cease working altogether wherever it was available as part of the edit interface.
