Google Docs in a clean-room browser
> seems to compare the Firefox version number with 65 ... I’ve no idea what the purpose of this is<p>I previously worked on JS infra at Google.  Google uses a lot of shared JS libraries that date back over a decade, and those libraries have accumulated lots of workarounds for browsers that nobody cares about anymore.  (One especially crazy seeming one from today's perspective is that there's a separate implementation of event propagation, I believe because because it dates back to browsers that only implemented one half of event bubbling/capture!)<p>It's very difficult to remove an old workaround because<p>1. it's hard to be completely sure nobody actually depends on the workaround (especially given the wide variety of apps and environments Google supports -- Firefox aside, Google JS runs on a lot of abandonware TVs), and<p>2. it's hard to prioritize doing such work, because it's low value (a few less bytes of JS) and nonzero risk (see point 1) without meaningfully moving any metrics you care about.<p>In all, how to eliminate accumulated cruft like is a fascinating problem to me in that I can't see how it ever gets done.  And it's not a Google thing.  Even the newer cooler startup I now work at has similar "work around old Safari bug, not sure if it's safe to remove" codepaths that I can imagine will stick around forever, for similar reasons.