Is Gmail tied to IE?

Something wierd happened today… I use both IE and FireFox on my laptop. Also, my office WiFi uses a proxy and Home WiFi doesn’t use one. So, everyday when I come home and try to connect to the internet, I have to uncheck the USE PROXY CONFIGURATION options in the network settings in the browsers.

Today I came home and unchecked the proxy option in FireFox and opened gmail and composed a message. So far so good. Then when I tried to attach two files to the mail, It failed. It tried multiple times using the RETRY link and yet nothing worked.

Then out of sheer doubt I opened IE and unchecked the proxy option. Then came back to FireFox and hit the retry link. Guess what? It works now!!

Question:

1. Is firefox using IE settings for file upload?
2. Or is somehow file uploading in Windows closely coupled with IE no matter which browser you use?
3. Or is this something that folks at Google missed or wanted us to ignore?