Try the Firefox Safe Mode to see how it works there. The Safe Mode is a troubleshooting mode, which disables most add-ons.

(If you're not using it, switch to the Default theme.)

• You can open the Firefox 4.0+ Safe Mode by holding the Shift key when you use the Firefox desktop or Start menu shortcut.
• Or use the Help menu item and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Don't select anything right now, just use "Continue in Safe Mode." To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before using the Firefox shortcut (without the Shift key) to open it again. If it is good in the Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one.

Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.

When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.

Nathan thank you, but problem is still same in safe mode. It is same problem after disabling all plugin as well. IE32bit/64bit have same problem. Only Chrome works fine.

hello ZPipinic, firefox has introduced a new protocol named SPDY that should make pages load faster and is used on google pages. i've seen reports by some other users who had the same problem uploading attachments to gmail as long as spdy was enabled.

could you please try the following: enter about:config into the location bar & search for all preferences beginning with network.http.spdy.enabled - please toggle all of those to false by double-clicking it & restart the browser.

Madperson thank you, but it is still same problem. Now uploading is liter bit longer before fail. It looks on progress bar like starting upload from beginning several times and on the end fail to upload attachment.

Certain problems can be solved by performing a Clean reinstall. Please follow these steps one by one and tell us if it helped:

1. Download the latest Firefox from http://www.mozilla.com
2. Close all Firefox windows by going to File > Exit, confirm all upcoming messages.
3. Now, uninstall Firefox by following the steps mentioned in the Uninstall Firefox.

IMPORTANT: The uninstaller has the option to remove your personal data and settings. Make sure that you do not check this option.

Once this is done:

1. Go to Start > Run, enter %PROGRAMFILES% in the textbox and press Enter. An Explorer window should open.
2. In the Explorer window, see if you can find a Mozilla Firefox folder. If you do, right-click it and select Delete. Confirm that you want to move the folder to the trash.

Now, go ahead and reinstall Firefox:

1. Double-click the downloaded installation file and go through the steps of the installation wizard.
2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

Please report back to see if this helped you!

1. Uninstalled Firefox 15 and delete folder in program files 2. Run CCleaner 3. Installed Firefox 15 4. Same problem

1. Uninstalled Firefox 15, delete folder in program files and delete all personal settings 2. Run CCleaner 3. Installed Firefox 16 4. Same problem 5. Uninstall Adobe flash player 6. Same problem 7. Reinstall Adobe flash player 8. Same problem

Portable Firefox 13.0.1 & 15.0.1 running from USB disk same problem Portable Chrome 19.0.1084.56 working fine.

I try portable Firefox and portable Chrome on other computers with Win7 and XP still same problem.

Which security software (firewall, anti-virus) do you have?

Did you make sure that it isn't causing problem with uploading files?

Try to boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that works.

After I try Firefox with Windows in safe mode as you suggested and Firefox problem was still same I try something else: I try portable Firefox on my sister computer (another house and another Internet provider) and Firefox was working fine. Since I have 2 Internet providers (one slow with flat rate and another 2Gby limited but quickly) I change Internet provider’s rutter login user name/password and Firefox starts working fine on all computers and Firefox versions. Monday morning I’ll contact Internet provider and ask for reason that cause Firefox (but not Chrome) to upload normally attachments in Gmail. Thank you for your help and suggestions. I learn something as well.