Opera 8.51
I'm browsing today with Opera 8.51 instead of Firefox. 3.8 meg installer. Blindingly fast install. 5.3 megs on disk. Snappy page loads. Much better email client than Thunderbird.
The appearance and operation are taking a little getting used to. Opera zooms the whole page with the "+" and "-" keys. Firefox changes only the text size. There's no keyboard shortcut for opening a link in a new window. Even my links page opens new tabs, not new windows. It doesn't auto-size large images. Pressing the "Return" key when a form is focused on a radio button doesn't submit the form, a shortcut I've been relying on for my Drupal blogging.
On the plus side, the "back" button goes right back to a form fill-in, instead of offering to repost. A trash icon pops up a menu with every page you've closed in your current session, including unseen pop-up windows. And they're going to integrate Bittorrent in version 9.
But I'm going to switch (back) for a while, and see what I think. Firefox will still be there when I need it.