[bugfix] Fix FireFox profile folder path for macOS

[RalphORama]

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I recently opened issue #8898 regarding --cookies-from-browser firefox:<profile> on macOS. When trying to find a Firefox profile on macOS, yt-dlp was looking in ~/Library/Application Support/Firefox/ instead of the proper path, ~/Library/Application Support/Firefox/Profiles/.

Firefox has used the Profiles/ subdirectory to store profiles on macOS as far back as 2016 (and probably earlier than that, this was the first result in a Google search), so this is likely a bug on yt-dlp's part that has gone unreported.

Fixes #8898

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