This commit adds a test for 0603d1ac1843bc4098d74382beda6cc511350ccd. Before the fix the `pagerendered` events would be fired just 2-3 milliseconds after the call to `increaseScale`/`decreaseScale`.
The goal of this patch is to fix the test: https://searchfox.org/mozilla-central/source/toolkit/components/pdfjs/test/browser_pdfjs_zoom.js It's a regression due to #17790.