There could still be a version of Mozilla's Seamonkey around that could work.
According to the info in the download link it should run on win98, although I don't really believe it.
But if I switch browsers, I will need something similar to No Script that will work with a new browser and Win98SE. The main problem that I see is that you are constantly going to run into what you are experiencing now.
Reason being is that old Pentium II processor simply cannot handle all of today's advertising. Today's infrastructure doesn't work with the "ancient" Win98 OS.
I have a start up disk for windows 98 and would like to update my 95 computer, but it states: there is another operating system on your computer so you need a windows 98 update disk. If you do upgrarde to XP you'll need to check your system hardware and make sure you meet the minimum requirements -- in particular your RAM and your Processor.