I've noticed in the past few days a bold line in some wiki tables that were not there before and only appear in Firefox 3.1.1 and not IE8, 9, 10, 0r 11. Any ideas?
I checked the table's Wiki-code. It is fine at those horizontal lines' locations. There was an unrelated typo in another place. Everything else looks good for that table.
I can recreate that bold-line situation (seen in your image) by adjusting the FireFox browser's zoom rate, by pressing and holding the keyboard's CTRL key and scrolling the mouse-wheel. At different zoom rates, different lines will appear more or less bold.
Zoom-in far enough and the lines all seem uniformly bold.
Zoom-out far enough and the lines all appear uniformly thin.
Aha! That was it. I noticed the page width on the wiki pages had a scroll bar at the bottom (left - right) and thought that strange but didn't make the connection to the bold line problem. I must have accidentally put my browser in that state. They did an update to FF in this time period also so I thought maybe that's what caused it. Thanks!