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Why is firefox slow to load a heavy JS file?

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  • Last reply by jscher2000

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I'm trying to troubleshoot some poor firefox performance. The following page:

is extremely slow to load in firefox (tested on linux and mac, firefox 64.0), pegging one of the firefox child processes at 99% cpu for several seconds. The same page loads quickly in both chrome and webkit. The cause, I suspect, is some relatively heavy js (about 45 MB). It's not the transfer of the JS, since this happens when even once the JS is cached.

So, sub-questions:

A. Why is this happening? B. Can it be fixed? If so, how? C. If this isn't the right forum, is there a better place to ask?

All Replies (3)

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45MB sounds like a lot of code.

I don't know whether this tool is useful:

You can get help from the developer tools team here:

More generally, see: Where to go for developer support

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Thanks, that is helpful. Profiling reveals that about 90% of the load time involves "Idle" - image attached. That's a clue, at least. Is this in the vicinity of a known issue with Firefox 64.0?

This application loads quickly in other browsers, and has loaded quickly on previous versions of Firefox.

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Sorry, I don't know the significance of those categories. I would refer you to the documentation and forums I mentioned before.