If you use Thunderbird like I do you may have noticed that HTML emails cause it to freeze momentarily. For a long time I thought this was a side effect of a large mailbox file and large email size but nope, it has an official bug.
The problem is fixed in Thunderbird 3 which hasn’t been released yet but there’s a simple way to avoid the problem. Open your address book.
It appears that having your address book in memory helps Thunderbird to render HTML emails quickly. I don’t know why, and the bug has some interesting comments on why. It’s possibly related to the anti-phishing code in the email client.
If you don’t want to keep your address book open all the time install the Contacts Sidebar plugin. HTML emails now render instantly.
I’ve lived with this bug for years. It’s a huge relief to have it “fixed” now!