It's a stick on to be this game v Hibs in 1998/99.
http://www.stmirrenprogrammes.co.uk/StMirren/STM_Match_Details.php?Season=1998&GameID=199901090
TV footage from 98/99 (e.g. 1-5 v Morton ) shows exactly the same layout of advertising round the pitch, which is different from other seasons.
We were barely getting over 2000 for a lot of games that season, so the busy stand points to the Hibs game where there were over 6000, as does the hint of white on the grass (9th January type weather).