You can set browser.download.start_downloads_in_tmp_dir => true in about:config to make Firefox use the OS temp folder for downloading and opening files.

You can open about:config via the location/address bar. On the warning page, click "Accept the Risk and Continue" to open about:config.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

That is the exact opposite of what I want. It's already set to false and I'm still not getting prompted to save files where I want them.

ithinktfiam, have you tried unchecking the option, restarting Firefox, rechecking it, then restarting again?

What security software do you have in case that is interfering?

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click "Refresh Firefox" in the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

@cor-el, I'm using standard MS Defender and the only Extension I have installed is an ad blocker.

@TechHorse, yes. This problem has been happening since I got the new machine a couple of months ago. I asked before, got that suggestion, it didn't work, and nobody responded with anything useful.

ithinktfiam, something else to try, if you haven't already.

Untick Always ask you where to save files. Select a different "Save files to" location other than the system downlods folder (or perhaps any system folder for that matter). Download a few files to make sure that they are going to this new alternative location. Recheck the "Always ask you where to save files" option. Once again, Firefox restarts inbetween steps can't hurt.

I'd already done that @TechHorse, but, just for S&G's, I tried again. The usual failure.

Does anyone have a real solution?

ithinktfiam, have you tried testing in a new profile, without importing any data or making any changes beyond enabling the save prompt (if necessary)?

Some other things to consider / try.

Do you normally initiate downloads by left-clicking on a link, or by right-clicking and selecting "Save [item type] As…"? Does trying the other way bring up the save prompt?

Do you normally initiate downloads in a normal or a private window? Does the prompt appear in the other window type?

Have you been testing similar types of files with a smaller group of websites? Sometimes Firefox can remember download settings for specific filetypes and / or sites. To rule this out, do you still not get the prompt with completely new sites, and / or a variety of item types (links, images, zips, setup files etc.)?