It's not a question of avoiding updates altogether, but the sad reality that it always seems to choose the most inconvenient and/or expensive time to do it. If they'd just do as Thunderbird does -- notify me that there's an update and ask me what action I'd like to take -- there'd be no problem. As it is, being unable to choose when the update happens is unacceptable.

FWIW I've tried every documented setting, "enterprise" policies, etc. to prevent automatic updates in FF, but nothing seems to stick.

Yes it has its pros and cons like everything. But as a default for the average user I think auto update should be enabled