Are userscripts still run once after page load? That was a major pain point last time I tried using them, on a dynamic page. I tried hooking some events and run

Are userscripts still run once after page load? That was a major pain point last time I tried using them, on a dynamic page. I tried hooking some events and run-registered-function-on-tree-change-but-at-most-at-N-msec-intervals, but it got out of hand and ended up looking to take much more time to write than the handler it was going to call, so I filed it under "should be written once and properly" and postponed the whole thing.