eBay, PayPal, and a lot of the internet at large no longer support Internet Explorer well, or in some cases at all.
Your choices are to complain about it, or if nothing else, use another browser for tasks that IE can't perform like Firefox or Chrome.
I still use Firefox 2.0.20 for most of my searching and general poking around because I have that browser tweaked the way I like it. FF2 was obsoleted 10 years ago, and recently is having a lot of trouble as websites are bumping up security requirements to even connect, and FF doesn't support TLS 1.1.
Because FF2 started breaking on eBay about 6? years ago, I partially moved to FF3.6, which I still use for 75% of my eBA, PayPal, FedEx, etc business, along with other sites (I run 3 different instances of FFF3.6.24 , configured differently for different tasks and purposes.) Things like leaving feedback, my seller dashboard, the listing bulk editor, and some other things are partially or totally broken in FF3.6, so I use an instance of FF31 for those. Additionally, as FF3.6 also does not support a minimum TLS 1.1 security protocol, I have to use FF31 for these forums and for other sites that balk in FF2 and FF3.6.
When things on a given site just wont work in FF 31, I fire up an instance of FF40 or FF52 and do my business there.
When buying on eBay I use Firefox 3.6.24 and stick things in the cart because I like it better and have it customized with addons for printing listings, etc. I then have to jump over to Firefox 31 to checkout since PayPal broke the interface a while back for FF3.6 browsers. Not a big deal since both are always open and logged in.
Why? I like the way I have my old browsers customized, extremely dislike the new Firefox interfaces and methods, and just haven't taken the time to just tweak Firefox 52 to suit to buy a few years of breathing room.
You have to use the right tool for the job. And the newest shiniest version isn't always the right tool (newer Firefox versions won't store and/or use form history for saving and recalling eBay feedback comments, and other similar issues, whereas Firefox 3.6 and Firefox 31 have no problems with those things).
I personally like portable versions of Firefox (I have 17 versions/22 instances installed) as they are self contained and standalone. Firefox Portable 52.6 ESR is a solid extended support release that avoids some of the issues of newest versions while being current(ish?) security wise.
https://community.ebay.com/t5/Selling/Form-history-not-saved-on-ebay/m-p/28110271/highlight/true#M11...Just use a different browser for checkout.