Well, I have tried every installation possibility, both before William's last post and since. Stand doesn't work for me. The 'Don't animate gifs'box is checked, but also greyed out, and it has no effect. Saft and Pith Helmet say on their webpages that gif animation blocking doesn't work on Safari with their products.
Anyway, I'm happier with Firefox now than I was with Safari. It's a lot quicker, and with the plug-ins NoSquint (for text size with a setting for each site), AdBlock for Flash, and NoScript for Javascript (which despite its name gives a lot of control over the display of Javascript), I can manage sites a lot lot better than I ever could in Safari.
In Safari, I had to use the text resize buttons in the toolbar all the time, and I toggled plug-ins and Javascript a lot. Now that I have used Firefox for a couple of weeks, I rarely have to do anything - I get the stuff I want and I don't get the stuff I don't want.
The downside is that I used 'save as webarchive' a lot, and I also copied and pasted whole articles to TextEdit. Webarchive doesn't exist in Firefox, and copy leaves out the pictures and formatting, unlike Safari. So, what I do is to keep Safari in the Dock, and when I want to Webarchive or copy, I drag the Firefox address bar to the Safari dock icon and save or copy the page, and then close Safari. I still do a lot less clicking than with Safari alone, and most of the time I have a smooth browsing experience.