The Firefox installation should not have given you any problems but it will require JAVA for many websites to work. (It does support W98)
You still need IE for Windows Updates though.
Do you have all the available Windows Updates for your op system?
I would suggest a HJT log at this point.
scrrun.dll
scrrun.dll - Here is the scoop on Microsoft Script Runtime Library as it pertains to computer network security. The big question: what is scrrun.dll and is it spyware, a trojan and if so, how do I get rid of Microsoft Script Runtime Library?
scrrun.dll (Microsoft Script Runtime Library) - Details
The file scrrun.dll, is used by windows when running scripts such as those written with JScript or VBScript. If scrrun.dll is unavailable, windows will not be able to execute scripts. If you do not use any scripting on your computer you may be able to remove this file.
scrrun.dll is flagged as a system process and does not appear to be a security risk. However, removing Microsoft Script Runtime Library may adversly impact your system.
The Spy Bot database currently registers scrrun.dll to Microsoft.
This is part of Microsoft Windows.
scrrun.dll is related to jscript.dll, pdm.dll, selfcert.exe, vbscript.dll.
Whenever you have a concern about a file like scrrun.dll, feel free to visit our free spyware removal page to help verify your file is not a security risk.
The Spy Bot database is updated often, but inaccuracies may still exist, often caused by viruses named after valid files such as Microsoft Script Runtime Library. Always verify your results just to play it safe.
http://www.auditmypc.com/process/scrrun.asp(If scrrun.dll is missing you have a problem with your Windows installation)