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 isI 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!)It's very difficult to remove an old workaround because1. 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), and2. 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.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.