If you want to change the email client that Mozilla launches when an email link ("mailto" link) is clicked then:
Launch Mozilla and enter the URL about:config and hit Enter.
Control-click (or right-click) on any list entry and choose the New pop-up menu, and then the String sub-menu. In the first pop-up that appears, put applications.mailto. In the second, put (for example), the path to the OS X Mail application: file:///Applications/Mail.app/Contents/MacOS/Mail
Control-click on any entry, and again select New and String. Put applications.mailto.parameters in the first pop-up, then put "%url%" in the second pop-up.
Control-click on any entry, but this time select New and then Boolean. Enter network.protocol-handler.external.mailto in the first pop-up, and then put true in the second.
Most of you may know already that the final version of Safari introduces Auto-Tabs. An Auto-Tab is a folder of bookmarks that behaves as one bookmark -- when clicked, it will open all the URLs in the folder in separate tabs. To enable Auto-Tabs for a folder, open the Bookmark view and then find the folder you'd like to modify, and then just check the Auto-Tabs box. Once checked, the little triangle in the folder's name will become a little square, and now your folder acts like a single URL bookmark. Quite handy.
But what if you want to access just one of the URLs in your new auto-tabbed folder? To bring back the dropdown menu, just press Option key before you click on the auto-tabbed folder; you'll get the standard dropdown list of all the URLs in the folder.
[robg adds: I found that the Command key also works to display the dropdown menu.]
I felt that the default text sizes in Safari were too large for my liking, but reducing them in the Prefs resulted in quite a few sites showing small, unreadable, and non antialiased fonts in places.
In an attempt to fix this, I looked into the preferences for OmniWeb and copied the following lines into Safari's plist (~/Library -> Preferences -> com.apple.Safari.plist):
[robg adds: I had done this for a while, but found that I preferred having the Command-1 through Command-9 shortcuts (for the first nine items on the bookmarks bar) functional instead. With dividers, you'll give up some keyboard shortcuts, but it may be worth it if you're primarily a mouse user...]
I like having the Address bar hidden in Safari. This saves space. When the address bar is hidden, you can press Command-L to show it and enter any URL, and when you press Return to confirm it, the Address Bar automagically slides away.
Furthermore, when you open new tabs/windows, you can enter URLs even though the Address Bar is hidden. This might be considered a bug, though.
[robg adds: How very odd -- you can, indeed, enter URLs with an invisible address bar on a new tab or window!]
After seeing the recent hint about browsing local disks to view html help files with a web browser, I'd like to suggest that readers could go a step further by turning one of the excellent free browsers available for OS X into a dedicated help viewer. I've started doing this with Navigator / Chimera / Camino, so that I have a way to prevent HTML help (like that provided for most Adobe apps) from hijacking my default browser. I've done this by seeking out the index pages of the help docs I want to include, and bookmarking them in Camino. Note that some of these pages are hidden inside application packages and you may not be able to access them by navigating with the browser. In these cases, you will need to Control-click on the package in the Finder, choose 'Open Package Contents' from the contextual menu, locate the required help page, and drag it manually into the browser window. If the business of hunting down the help pages for yourself is too intimidating, simply make the browser you've selected as your help viewer the default browser temporarily, launch each of the apps whose help you want to include, call up the help, and bookmark the page when the browser comes to the front.
An alternative to simply bookmarking help pages is to create your own HTML page with links to the desired help, and make that the browser's default home page. This is what I've done with Camino and it works really well. Using a browser in this way allows you to fine tune window size and other display settings specifically for viewing help files; your default browser can be left the way you like it for browsing the web, and won't have it's 'history' bloated by the dozens of help pages you were looking at while you tried to track down the key combo for creating perspective distortions in Illustrator.
Some help files intended for viewing in Apple's hideously sluggish Help Viewer can also be viewed like this, but may not function correctly. For the record, my Camino personalised help viewer links me to help files for Illustrator, InDesign, Photoshop, LiveMotion, Revolution, Snak and File Buddy, with additional links and bookmarks that lead directly to specific sections of the help docs. Go for it. It's a cinch to set up, and a lot nicer than forcing your default browser to moonlight as a help viewer.
As an alternative to the Finder and the Terminal, you can use Internet Explorer to browse the file system. Just type in file://local and you will see all files, including all hidden files. You can enter application directories (the ones ending in .app) if you want to. If you have different partitions, you might want to use file://local/volumes to access them.
If you do this in Safari, it will open a Finder window. In Netscape, it doesn't do anything (robg's note: In Netscape products, it should work with three slashes, as in file:///Applications).
I use this feature to access help files. I go to the application's folder, and search for a help folder. Most help files are plain HTML, so just click on one, and suddenly you can view the help files -- this is superfast compared to the Help Center.
[robg adds: We've run hints on browsing local files before, but I thought using the browser to both browse and open the help files was a unique concept.]
The most recent nightly builds for Camino include a very convenient text search feature: after your page loads, just begin typing your search string and Camino highlights the first occurrence of the string on the webpage. You can subsequently press Cmd-G to search for further occurrences of the string. This feature saves a trip to the Find dialog box.
[robg adds: I generally stay away from hints on "unreleased" software, such as the nightly builds from Mozilla or Camino. However, this hint has been submitted at least five times in the last couple of weeks, so I'm going to run it. You can download the nightly builds via the above link. You should be aware, though, that the nightly builds may occasionally be less stable than the officially released version.]
[robg adds: Big5-HKSCS is a special supplement to the standard Big-5 character set for use in Hong Kong. Taken from the application to IANA for the extension, the official description is: "To facilitate electronic communication in the Hong Kong Special Administrative Region (SAR), the Hong Kong Supplementary Character Set (HKSCS), a supplement to the standard character set of Big-5, was developed in 1999. This supplementary character set includes characters collected from various sectors in Hong Kong and represents a common set for the community. It has been widely used in Hong Kong."]
It seems that the latest update to QuickTime has gained rudimentary support for PDFs. Using Safari, try clicking a link to a PDF and rather than downloading, the PDF should display within Safari. Dragging and dropping a PDF on Safari also works. I see no sign of navigation for multipage PDFs, thus only the first page displays with no zooming control.
In the MIME Settings portion of the QuickTime system prefs panel, there is now a checkbox for PDF in the still images category.
One other QuickTime change I've noticed is that the QuickTime logo often displays briefly as a flash animation begins loading within Safari.
[robg adds: In order to make this work on my machine, I had to change the MIME setting first -- it wasn't enabled by default. After seeing how it worked, I quickly went back and disabled it! The PDF Broswer plug-in provides much nicer support for inline viewing of PDF files.]