The visual differences occur because IE 6 (I do not have IE7 to test) does not seem to apply border to rows, only to cells, and also does not understand some of the more advanced selectors you have used, such as XSLT-ish select by attributes, or by child and adjacent sibling. I am a new user to solr, but this seemed like a low-risk area where I could pitch in and help.
This proposed patch puts the relevant css information into regular css classes, and then adjusts the jsps to match, e.g. instead of
tr > td[name="highlight"]:first-child
The meanings are slightly different, and they apply to a broader range of HTML, but it improves the look in IE and did not seem to have any negative impact in Firefox 126.96.36.199. I did not migrate every css2 selector over to a class this way, but just those that made a large difference in the way IE6 rendered the page without resorting to css hackery.
If I missed any locations, or their are awkward results in this style, feel free to comment. I purposely did not make any effort to modify tabular.xsl, as this thread indicates it is deprecated: