Form won't submit on Linux box

Has anyone experienced anything like the following and discovered why it occurs?

HTML form submitting to PHP script.

On Windows (Chrome 4, FireFox 3.5, IE7) the form submits fine.

On Linux (FireFox - not sure what version, 3 or 3.5) after submitting, nothing happens and it eventually times out.

Sorry, I’m not sure what version of Linux it is, but if it will help let me know and I will ask.

I should add that other forms on the same page do submit OK on the Linux box.

All the forms are to do with shipments. Each form represents a shipment and has a number of rows each representing a line item in the shipment. The forms are dynamically generated and are identical in structure. Each line item has a text input field where a note can be entered and saved by submitting the form.

On a recent example, there were three shipments on the page, one form for each. On the Linux box, the user could submit the first 2 forms, but not the third. Using Windows box, all 3 could be submitted.