Persistant internet problems – internet icons, dwindling speed, connec

Since I got proper wired ADSL I am having several problems when connecting, surfing and downloading from the internet. What the causes might be I don’t know but I’ve listed them below:

1) When I click my Firefox icons, be that on the desktop or on Rocketdock, it can take up to 30 seconds or so to physically open a page. I’m talking just a page itself, not content.

2) If I have just turned the computer on then the page loads pretty quick, that’s a webpage not a physical page. However, the longer I’m on the internet the slower the page load times seem to get.

3) This also manifests itself in downloads. When the computer is first turned on downloads are working fine, however, as time goes on, most downloads dwindle to nothing or all are not downloading.

4) When I click the Internet Explorer icon(desktop or Rocketdock), it opens on my homepage but if I enter an address the address opens in a new Firefox webpage while the IE page stays on my homepage!

Any help and advise would be greatly appreciated.