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Trello boards don't load in Firefox after Mac migration

Hi all,


I just got a new Macbook Pro and migrated all data from ym old Mac via Time Machine. Now all Trello boards don't load in Firefox, but they do load in Safari. In firefox, all I see is a grey page with a waiting animation and some parts of the Trello header.

Cache was cleared, cookies deleted, ad blocker is inactive, network filter deactivated - no solution.

Any idea what I could do?

Thank you and best wishes,




1 answer

1 vote

Can you try loading trello in a new Firefox private window?

yes, this works!

Like Flavio Fernandes likes this

But it would be great to have it in a standard window as usual...

Like Flavio Fernandes likes this

The private window turns off your browser extensions.  One of your extensions is preventing Trello from loading (I don't know which one, but I'm certain it is something that is installed outside of Trello in the browser).

Like # people like this

Thanks! I will check this out on Monday when I’m back in the office.

Strange that it worked on the old Mac. I haven’t changed anything about Firefox extensions, I only migrated to the new Mac...

OK, so I tried. Deactivated all AddOns and re-started Firefox. Result: none. Trello still doesn't load :-(

I guess it could be related to some kind of profile settings in the default window (localstorage or cache?)


It’s for a different app but there are instructions here for local storage clearing in Firefox:

Thanks, I did that - no change. I found this in the Web Developer console, not sure if this is helpful:



Maybe try loading that trellocdn url in the error message?

Clicking the file name in the message obviously brings up the souce code...



I have the same exact issue. The private tab does the trick.

I tried removing all cached data and yet have had no success.

I'm having the same symptoms of Trello not loading in Firefox. Loading Trello the first time works when Trello's service worker is not yet registered. But after the first load, the service worker is registered and all subsequent loads fail with the following in the console:


Using private window helps because the service worker will not be used: ”In Firefox, Service Worker APIs are also hidden and cannot be used when the user is in private browsing mode.” (Source:

It would be great to have a real solution to this and not need to work around with private browsing or disabling service workers completely.

OK, seems to be a serious issue. Trello, is there any solution coming?

I just found that LinkedIn has a similar problem. Loads only in private windows in Firefox on my new Mac.
All this sucks big time.

Further, I can't log into my Google accounts. It stalls after the dialog where the email address has to be entered. Works in private window. Must be a Firefox issue under macOS Catalina.

Problem solved - I created a new Firefox profile and migrated all important data from the old profile. Works.

Seems that Firefox has problems with pages that use asynchronous Javascript after a migration to a new Mac. It's not caused by the new OS (Mojave -> Catalina) on the new Mac. I just had the same problem when migrating an old Mac to a new one, both running Mojave.

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