Try to start Firefox in Safe mode. This mode disables all extensions, user customizations, hardware acceleration, etc. temporarily for diagnostic and troubleshooting. If Firefox works fine in Safe Mode, then this is likely an add-on issue. Restart Firefox in normal mode, then type "About:addons" (without the quotes) in the address bar. Disable your extensions one by one, restarting Firefox between each one, until you find the trouble maker. Once you do, you can disable that add-on and report the issue to that add-on's developer.

Can you hear other sounds in Firefox?

See the following article for more help on Safe Mode:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

The Google Translate page uses a Flash plugin to play the audio, so make sure that you aren't blocking Flash.

Also try updating all your Firefox Plugins using the following link:

• http://www.mozilla.com/en-US/plugincheck/
• When Downloading Plugins Update setup files, Remove Checkmark from Downloading other Optional Softwares with your Plugins (e.g. Toolbars, McAfee, Google Chrome, etc.)

After updating your Firefox Plugins, Restart Firefox.

Check and tell if its working.