Does the site have any indication that it doesn't support Firefox or other browsers other than IE?

Is this a new problem in Firefox 12, or did you have it in earlier versions?

When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

1. Clear Firefox's Cache

orange Firefox button or Tools menu > Options > Advanced

On the Network mini-tab > Offline Storage : "Clear Now"

2. If needed, delete the site's cookies here

While viewing a page on the site, right-click and choose View Page Info > Security > "View Cookies"

Then try reloading the page. You likely will have to log in again.

Does that help?

i have use firefox for the past year or more on this site and up to the last week i never had a problem, i have clear firefox cache and site cookies, plus clear history etc disable firewall, and antivirus but still nothing, i contacted host server and they responded with no problem on their end.

To see whether it is an interaction or incompatibility between Firefox 12 and one of your add-ons or custom settings, you can test whether the uploader works in Firefox's Safe Mode.

First, I recommend backing up your Firefox settings in case something goes wrong. See Backing up your information. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.)

Next, restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled

In the Safe Mode dialog, do not check any boxes, just click "Continue in Safe Mode."

If the uploader works in Safe Mode, this points to an add-on or custom setting as the problem. Any luck?

Note: If it is a Flash uploader, I don't know whether it will work in Safe Mode.

thanks for your useful help jscher2000. I gave up on the problem after trying your advise etc, went to bed & woke up this morning and everything seem to be working just fine now. not sure what we done to fix it but something must had worked.

Firefox needed a night off? Glad to hear it's working again.