Hi Winter
With Chrome I can't reproduce the problem you have.
So I chime in to tell you it IS YOU!
No seriously I hope this problem will be solved soon for you it sounds very inconvenient!
It's almost certainly your problem.
It does not necessarily have to be the Firefox (Chrome, Opera, whatever) installation.
Spyware can get in the way (note that most spyware is NOT a virus and, so, not detected by your AV scanner .. for that you need a spyware scanner). I have see this in the wild, but would judge it to be low likelihood.
More likely is that there is a problem in the registry.
Things to try:
Click the Start button (Windows Logo). In the Search box type "http://www.google.com/" then press Enter or the Search spyglass. If the Google web site does not come up, the problem is the registry. Repeat with the link to the KittyCatS site. If Google works and KittyCatS does not, come back.
You can usually fix this sort of problem by clicking the the Start (windows logo) button and selecting "Default Programs" on the right.
Click on "Set your default programs".
Select a browser which is NOT your browser from the list. Then click "Set this program as default." Then click OK and close the window. The idea here is to change away.
Go back to Default Programs, and set your normal browser as the default. This sets it back where you want it.
Re-test from the Search box and, if that works, from your Second Life viewer.
Moot point.
Just started working on its own.