If Google Chrome works for you, there is no harm in using it, but we don't support it.
For what it's worth, our developers all use Firefox so that should tell you something. If the guys who wrote the system use a specific browser...I'm just sayin'.
We haven't changed the image uploader recently, and we don't know of anything that would be causing an issue with it with Firefox. I'm not saying there could not be a problem on our side..it is possible...but we are not seeing anything in our incoming support cases for the image uploader suggesting a widespread problem.
Most of the time, it is something on peoples local machines that cause problems with the uploader.
The image uploader running in Firefox depends on a component being installed on your computer called Java Runtime. If you have auto update turned on on your computer, Java will update itself periodically. I have personally had seen these updates fail (I have no idea why), with the failure messing up the Java runtime and with it, the image uploader.
You can uninstall Java (use your 'Control Panel to find the program (see the Programs and Features option) and run the uninstall for it). Then reinstall it from this link. This gives you a clean Java install, and the image uploader should work, everything else being equal.
By the way, the latest Firefox version is 7.01. Most people will be best off to be running the latest version.
Hope this helps. If you are still having difficulties with the uploader, my advice is to file a support case--or another support case if you already have filed on--and have them keep working the issue with you.