Profiler import hangs with Conex (an extension) enabled

Conex is an extension that somewhat reimplements the old Firefox tab groups/panorama using containers. Each container is a group, and when you switch between active groups, it shows only the tabs in that group and hides all others.

AMO: https://addons.mozilla.org/en-US/firefox/addon/conex/
Source: https://github.com/kesselborn/conex

If I have Conex enabled, when I finish capturing a profile, the tab for profiler.firefox.com gets opened but it hangs at importing for at least 20 minutes. This is consistently repeatable for me even with a new profile with Conex added and only the default container with a single tab. If I disable Conex, the profiler works immediately and as expected. Nothing looks relevant in the profiler site's console or in the browser console.

I'm running the last release of Conex from AMO on the current nightly on Windows 7. Please let me know if I can provide any additional information.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-297)