In Firefox macOS, the Delete key (forward delete) has stopped working in the Save As dialog box popup

Copying this from a Reddit post as I have the same issue and looking for a solution: Recently in the past month or so, the Del/Delete key has stopped working in Firefox's Save As dialog box popup. Literally every other key works fine system-wide, and Del works in everything but Firefox's Save As box. To elaborate... Opening up the Save As box for anything in Firefox—a page, a file, an image, etc.—and trying to use the Del key to delete characters in the filename field just doesn't work. Backspace works fine, all other keys work fine. The only way to get Del to work in that scenario is by pressing Shift+Del instead, which is odd because it didn't used to be like that. I know the obvious answer is "Just don't use the Del key to edit a filename when saving files in Firefox" or "Use the backspace key insted", but I've been doing it this way for so long that it's pure muscle memory at this point. I've tested/confirmed that the Del key stops working this way in regular Firefox, private windows, and troubleshooting mode, so I don't think it's an issue with addons or extensions. I can't pinpoint anything else on the system that might be causing it either; it really does seem to be an inherent Firefox issue that's suddenly popped up.