I used to use Safari because of ecto. I used ecto because it has lots of cool features (such as pictures) and a cool AppleScript and bookmarklet combo to post to ecto from Safari. But then MarsEdit came out (and although it doesn't have WYSIWYG that's not a bug because the ecto WYSIWYG is great but doesn't work with nested lists which I use often via cut and paste from Omni Outliner so I can't use it. I really need to file a bug report with Adriaan about this)
I also realized that Firefox is much faster and I don't actually use the cool ecto features (I just use the HTML provided by Flickr for pictures now because it's no muss/no fuss and works well unlike the problematic (due to no fault of ecto) newMediaObject upload that ecto uses)
Plus, MarsEdit works with any browser not just Safari and MarsEdit works via a bookmarklet that doesn't use AppleScript. Therefore MarsEdit doesn't have the mysterious AppleScript bug that causes the ecto script not to work at random times.
Yes, Firefox eventually takes up a lot of memory but so does Safari. I just do what I did with Safari, and reboot Firefox every day.
I am eagerly awaiting Tiger and future versions of ecto. Hopefully ecto will have a bookmarklet in the future that somehow gets around the AppleScript bug (or Apple fixes AppleScript!), a WYSIWYG mode that works with the nested list HTML code from Omni Outliner and Safari will fix the applescript bug and become faster in Tiger. If that happens, I'll gladly switch back to ecto and Safari.
From Firefox Temptation.:
I live on a Macintosh, and on a Macintosh, the native browser is Safari, which is good. But a couple of times in the last week, I've cranked up Firefox for one reason or another, and I'm beginning to think it just may be better. Among other things, it seems to be faster. I'm about 80% of the way toward switching. Can anyone provide me with reasons not to?