What you need to do is some troubleshooting as links that are active for me using Firefox 10.0.2 are not active for you.
1. How are you connecting to the internet and to WordPress.com? The way you connect to the internet (mobile, satellite, DSL, dial-up) and to your blog, and how many proxy server jumps etc. it takes to connect can cause problems. There maybe be problems with your ISP and/or with the proxy servers. Can you access any of these directly?
2. Are you using http:// or https:// see http://en.support.wordpress.com/https/
3. Exactly which browser and version of it are you using? If you don’t know click here to find out > http://whatsmyuseragent.com/
4. Have you tried clearing your browser cache and cookies? http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=32050
5. Is your browser version up to date? You can upgrade any browser version here. http://browsehappy.com/
6. Have you tried using the browser with all extensions or add-ons disabled?
7. Do you have third party cookies enabled? http://support.google.com/accounts/bin/answer.py?hl=en&answer=61416
9. Do you have another browser you can try?