There are plenty of reasons why you could be seeing "odd" behaviour from your browser. But one factor that is always worth checking is your browser cache. 

When your web browser (Internet Explorer, FireFox, Safari etc etc) visits a page it will (depending on your browser settings) store a copy of that page and all the elements in it. Next time you visit the page, it will be able to pull the content out of its own store, rather than going back to the web site to view it again.

So you are actually viewing the page from this "cache" store rather than the actual page on the web. In good times, this speeds up your browsing and reduces demand on your network connections. 

But if you are having intermittent problems viewing a web page, or unpredictable behaviour, a good first step is to make sure that you are actually always viewing the live page rather than the cached content. For example, even if your browser can not connect to the internet at all, it might be (again depending on settings) it might be reading the page for the cache.

Clearing your cache might not solve your problem, but at least you will know for certain that you are actually connecting to and viewing the live page.

Here is how to do that in Internet Explorer and Firefox...

1. In Internet Explorer 8 (IE8), go to the Safety menu, click Delete Browsing History. Then select "Temporary Internet files and History", and then click Delete.
2. In IE7, select Tools, Internet Options, choose the General tab and under browsing history, click Delete. Then click Delete Files in the "Temporary Internet Files" options. 
3. In IE6, select Tools menu, click Internet Options and under the General tab, in the Temporary Internet Files section, click the Delete Files button.
4. In Firefox 3. Go to Tools, select Clear Private Data and then check Cache. Click Clear Private Data Now.