This has been a continual problem since Firefox 56 or 57. There have been no suggestions that have worked to correct this issue. If someone wants to check this out for themselves, log into eBay and start the process to list an item. When you see all of the drop down menus to select different things (like the item condition, etc.), you will find that the menus will NOT stay open (you have to click and hold the left mouse button to make your selection). I noticed that the drop down menus on this site won't function correctly, either. This is occurring with two bluetooth mice and a USB mouse as well. The operating system is MacOS 10.14.3. The problem does not occur in the versions of Firefox prior to 56 or 57 and the problem does not occur in Chrome. One thing I just discovered is that if I click at the very outside edge of the menus, they will usually stay open. I really would like to get this issue solved once and for all. Refreshing the browser does not change anything and neither does safe mode. I think there is some coding change within Firefox that is causing the issue. If anyone has any idea as to what might be causing this issue, please respond. Thanks in advance. P.S. It was suggested that I try a test profile or a new load. I have just finished a completely fresh load of OS 10.14.3 on a brand new SSD. NONE of my Firefox profile information was transferred (only my bookmarks). I transferred NONE of my computer user profile information, either - I installed everything from scratch and manually transferred all of my documents, photos, music, movies, etc. The problem is STILL happening on a completely fresh build of my OS.