Ideally this would work on all browsers. But honestly, Internet Explorer 8 came out in 2009 on XP and Vista.
en.wikipedia.org/wiki/Internet_Explorer_8
9 years is a lot in terms of internet technology. No one should be on the internet with Internet Explorer 8.
Making sure that even ancient browsers like this one are still supported would tie up valuable resources, which I don't think is worth it.
In the last year the world wide share of Internet Explorer was below 4%:
gs.statcounter.com/browser-market-share
This is based on ALL Internet Explorer Versions. I would assume that IE8 is probably somewhere far below 1%.
Alternative: Use a less problematic question format. The slider (together with the ranking question) is probably the most sensitive question format when it comes to function and display.