How to prevent 'opened files' (temporary files) saved in the Downloads folder
The latest version of Firefox is giving me a nightmare. Previously, when I downloaded something, an alert would automatically pop-up asking me whether I want to save the file or just open it. For those files which I only want to open them once, I would click Open. Then, I would either save the file into another format or copy the content to somewhere else and be done with it. Those 'Opened' file were just temp files which would be deleted automatically after some time. But since the previous update of Firefox, the option to 'open downloaded files as temp files' seems to have been completely gone. I've already manually change the settings for all types of files back to 'Always ask' but the files I 'opened once' are no longer just temp files but permanently saved in the Downloads folder. I personally seldom save things in C drive. Today I occasionally opened the Downloads folder and was astonished to see that all the 'temp files' I opened last month are all saved in there. It's very annoying. Why should I even be wasting my time to clear these temp files manually? The only reason I've been using Firefox over Chrome for these many years is because Chrome always forces me to save all the downloaded files to my local drive and doesn't provide me the option to open them as temp files. If Firefox has become just like Chrome, forcing me to save all unwanted files to my local drive, what's the point for me to continue using Firefox?
Opaite Mbohovái (1)
As you noticed, Firefox 98 changed from saving downloads in the Windows Temp folder for "Open with [relevant application]" or "Use [relevant application]" to saving them in your default downloads folder (the one next to "Save files to" on the Settings page). It's not possible to pass a file to an application without saving it somewhere.
Firefox 102 added a hidden setting to roll back that change. Here's how you access it:
(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.
More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.
(2) In the search box in the page, type or paste browser.download.start_downloads_in_tmp_dir and pause while the list is filtered
(3) Double-click the preference to switch the value from false to true