I think the first step would be to change the setting in the Options dialog, as described in this article: Startup, home page, tabs, and download settings. After that, Firefox should start keeping track of your recently used download locations and create those preferences automatically.

Does that work?

But to answer your question...

To create a custom preference:

First select and copy the exact name of the preference (e.g., from this page or a reference article).

Then in about:config, right-click an existing preference and choose New and then the type (these are String preferences).

Firefox should prompt you for the name of the new preference. In that dialog, paste (e.g., Ctrl+v) and OK that.

Firefox should prompt you for the name of the new preference. In that dialog, you could temporarily use C:\ if you don't have the full path handy.

To later paste in the full path, double-click the preference or right-click > Modify.

To get rid of a custom preference, right-click > Reset. You may need to close and re-open about:config to see this change.

It is possible that anti-virus software is corrupting downloaded files or is interfering otherwise.

Try to disable the real-time (live) scanning of files in your anti-virus software temporarily to see if that makes downloading work.

See:

• http://kb.mozillazine.org/Unable_to_save_or_download_files
• browser.download.manager.scanWhenDone = false

Thanks for your answers. Of course I first tried to settle in Tools/options/ general/downloads and couldn't get FF to do what he was told to. Also reset FF twice without any result.

I added the missing lines in about:config as you said but they disapear asa you close about:config. It's actually what's explained in the FF troubleshooting literature. I kept browsing in there to find the way to glue these 3 lines in but didn't succeed up to now.

Thanks also to cor-el. But I don't understand why my anti-virus (avast) I've had for a while now should suddenly interfere with FF. Unless one of the last Avast upgrades bugs with FF. I have some doubts about this as one can find complaints on FF concerning this issue since FF 27 . Do you have any information about this?

I'm not far from leaving FF as I can't work correctly anymore with it. Think I'll try going back down to FF26. And change if it doesn't work.

I have never seen that those prefs have ever needed to be added to Firefox. They have always been there.

I believe there is a regression Bug in Firefox 27 & 28 that is related to using a root directory location like C:/ when saving files. I do know that D:/ (my data drive) doesn't work now (tried that for another support question last week), but D:/foo does work.

As far as those 3 download preferences goes, are you saving "browsing and download history" or clearing "history" when Firefox is closing? Or using an external program to "clean up" your history?

As far as Avast is concerned, many add-ons provided by security applications contain binary components which need to be updated for every new version of Firefox. Changes to those add-ons, such as new features, can easily be added with no user notification about the change.

Hello the-edmeister and thanks for replying. I was also surprised to find these prefs had disapeared and I can't say how that happened. I remember I reset FF twice with the former version and I think another time with my last version 28 which means I already had this issue ("save as" not working) with the former version. So unfortunately I didn't check if these prefs were already missing or not with FF27. What does "foo" mean in D:/foo? As I have a second HD I could try using if there's a possibility. But I just checked: I couldn't change to D as nothing happens when I hit the browse button. Concerning my history options, except for "Always use private mode" which is not checked, all the others are. So "remember browsing & download" and "clear history when closing" are both checked. I run CCleaner about twice a month. Does this feedback give you any new idea? Thanks anyway

In case of use: I just poked in "Old FF Data" and found that both pref.js and sessionstore.js seem to have a problem. When I click them I have a "win script host" window popping up saying this (in french):

  For pref.js  - script C:\Doc...\old FF - Data \pref.js 

- line 1 - caractere 1 - erreur caractere incorect - code 800A03F6

- source erreur de compilation M$ JScript

  For sessionstore.js - same window except 

-line 1 - caractere 11 - erreur ";" attendu (means expected) - code 800A03EC

The same windows exactly appear when I call the same files in Doc & Settings/ my computer / Application data / Mozilla / FF / profiles.

Couldn't this have to do with the fact that FF doesn't seem to recognize my prefs?

You shouldn't double-click Firefox .js files like prefs.js and sessionstore.js because that will make Windows try to open them as a JScript files and these file are actually special JavaScript files that the JScript parser doesn't know about.
The sessionstore.js is a data file in JSON (JavaScript Object Notation format) and prefs.js contains lines to initialize prefs.

OK. I don't know this language. I guess if what I wrote above meant these files had a problem, you would have said so.

To open a .js file in Notepad for viewing and editing, you can right-click > Edit.

avast! may have a feature to override settings changes. Look for something called Browser Protection or Home Page Protection and disable it so you can save intentional changes. I can't recall whether this is in the main avast! software or it might be in the avast! Online Security extension settings.

Thanks. I don't use Avast's online security extension cause I have Outpost firewall beside. And found nothing like Browser protection or Home Page Protection in the main part. I feel I won't get further with this issue. I've copied my passwords and bookmarks and will uninstall FF completely before reinstalling it. If that doesn't work, I thought I would install a prior version but I have a doubt on this solution as some say it is risky. Any advice on this point? I saw a queer thing somewhere in the subjects covering this kind of bugs: it said if you can't get through with FF, then choose another browser like chrome or others. I thought it didn't look serious and said to myself perhaps M$ employees give advice in FF forums. Anyhow I'll let you know how things come up with my FF.

In case I've misunderstood the problem, could you clarify:

• Firefox downloads to a default directory even if you specify that you want to choose the location (what I was assuming)
• Firefox does not display the dialog to choose a location, so you cannot download anything

Concerning download choices in tool/option droplist: 1) FF does download in a default directory if I don't specify anything. Which means the first choice among the two possibilities. But I cannot choose the default directory as nothing happens when I hit the "browse" button.(No browsing box appears)

2) If I choose "Ask where to save" in download options, then when I need to download something and that I hit "save", well nothing happens, no browse dialog box appears.

Everything works fine if I use Internet Explorer.

I' ve completely uninstalled FF and re installed FF 28 first and then FF 27. Still doesn't work in both cases.

Really don't know what to do. Maybe FF 26 if I can still find it. I don't want to use chrome.

My OS is XP SP3.

Just tried after stopping Avast and Outpost Firewall: that makes no difference. Still can't get that box to choose where to download.

Oh, the Browse button doesn't work either? It sounds as though Firefox is not able to call up the Windows file/folder browsing dialog through either of those contexts. Maybe that is the underlying issue.

Two other Windows XP users reported the same problem recently:

• when trying to save a file, no file dialog appears (unsolved -- it works for a while after restarting Firefox then stops working for no apparent reason)
• File dialog (Save, Open, Export, etc.) does not appear in Firefox (unsolved -- More System Details also shows a disabled avast! extension)

You're right. Thats the point. The browse button doesn't work. I can download as long as there is nothing to choose about it.

Bloody issue! But I got it at last. I found FF 26 and the "save - browsing" box works again allowing downloads. I know it's a crooked solution to work with an old version but it's the best I found up to now.

I won't say the problem is solved as I hope a next version of FF will not have this same issue.

Thanks to all for your help. I'd be glad to know if you have anything new about this issue.

So it sounds like a change in Firefox 27 is not working with your system (and the problem continues in Firefox 28). But I don't know why it has resulted in 3 threads and not dozens; it must be something pretty specific.