Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All of them.

Start Firefox in Safe Mode {web Link} by holding down the <Shift (Mac Options) > key, and then starting Firefox. Is the problem still there?

Thanks for the quick response but safe mode and disable all add-ons still did not help. I wonder if there is any system thing got damaged that is used by Firefox but not by Chrome. (for I ran a virus scan before I found this and it did have some infected files) In the email sites the drag and drop files is still working. Only thing is those attach buttons when clicked you see the screen refresh but no dialog opens (same for the Firefox Download location Browse button)

That is possible, Lets find out;

Download Firefox Full Installer For All languages And Systems {web link} Save the file. Then;

Using your file browser, open the Programs folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Mac: Open the "Applications" folder. Linux: Check your user manual.

Look for, and rename any Mozilla and Firefox folders by adding .old to them.

Now run the full installer. If all goes well, remove the OLD folders when you are done.

Thanks, did what you suggested, still no opening dialog. it seems to me Firefox handles the opening of Windows file open dialog differently vs Chrome. I have another computer, the firefox opens the dialog with English title bar yet Chrome opens it with Chinese title bar. (both computer are running Chinese winXP SP3).

Hmm . . . Create a new profile. Then try to access those sites. At this time, don't change the profile until after the test.

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles Windows: 32-bit C:\Program Files\Mozilla Firefox\firefox.exe -p 64-bit C:\Program Files (x86)\Mozilla Firefox\firefox.exe -p Mac: Navigate to /Applications/Utilities. Open the Terminal application. In the Terminal application, enter the following: /Applications/Firefox.app/Contents/MacOS/firefox-bin -p Linux: In Terminal run: firefox –P For users who have one or more builds from mozilla.org this will not work. It would be best to have the full path so if you had placed the untared contents in a folder in /home it would be /home/<username>/foldername/firefox/firefox –P An easy way would be not to do it in a terminal but in say a launcher since you have to point it to the firefox script in Firefox folder you can then add –P on end. You can also have the exact "profilename" after the -P so Firefox will start with that Profile.

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Thanks again. the new profile did not solve the problem but I downgrade to 24.0 version and it worked (if I allow it to auto update, it will not work again) since another computer 34.0.5 works fine I think it is just firefox have different way of opening the file open dialog between 24.0 and 34.0.5 and somehow this computer the new way doesn't work anymore after the virus scan. I wish there is a good utility to find out the difference of these 2 computers. :)

Using an outdated program has risks. I've called the big guys to help you. Good luck.

You can try the following:

1. Try to change the download's folder to another folder in an admin account on that computer.
2. Make sure that the sites giving you issues are listed in the pop up exceptions: Open Menu > Options > Content (on the top) and Click Exceptions...
3. If you know where the file is listed, make sure to right click on the file and check the permissions of the folder.

Thanks, I did what you suggested as below:

1. Try to change the download's folder to another folder in an admin account on that computer.

> my problem is : In 34.0.5 I can't even open the Downloads folder with the Browse button <

  2 Make sure that the sites giving you issues are listed in the pop up exceptions: Open Menu > Options > Content (on the top) and Click Exceptions...

>yes, they are<

   3.If you know where the file is listed, make sure to right click on the file and check the permissions of the folder. 

> I guess you mean folder permission prevent the folder from opening but the attach button wont' work so I can't tell which folder the attach button would try to open first. All these was working before a virus scan so I am guessing some system files used by 34.0.5 (but not by 24.0) to pop the open file dialog got damaged? Please advise. Thanks again.

Start Firefox in Safe Mode {web Link} by holding down the <Shift (Mac Options) > key, and then starting Firefox. Is the problem still there?

Yes, and Safe Mode as Fred has suggested would tell you if its an add on.

Since it was after the virus scan, is it also possible that changes may have been made that keep Firefox from having access to that folder? If you think this is what caused it, disabling the antivirus temporarily and trying to access it would tell you. But its not, because Fred already had you do this, sorry for the redundancy.

The file that may have been corrupted: https://support.mozilla.org/en-US/kb/cant-download-or-save-files#w_delete... or if you also cannot open the about:downloads page you can try to reset Firefox (this will remove all add ons and changes to the about:config but put all the changed into a folder called "Old Firefox Data" Recovering important data from an old profile )

You could also try navigating to the downloads folder, right clicking and selecting properties. On the bottom right you can unblock the folder where it says unblock.

Other solutions are also listed here: http://kb.mozillazine.org/Unable_to_save_or_download_files#Res...