That's a really bizarre problem. I thought that being the local 'Mac guy' and helping set up and run a University Mac lab on a predominately Windows campus would have exposed me to pretty much everything that can go wrong. But, I've never heard of anything like this. So, I'll just offer some general troubleshooting advice.

Step 1: repair permissions, it's a long shot but it doesn't take too long and it's good routine maintenance. ( sudo diskutil repairPermissions / ).

Step 2: move the "~/Library/Internet Plug-Ins" folder to the desktop. If that solves the problem try removing anything that looks like it belongs to one the plugins in that folder from the "~/Library/Preferences/" folder. If the folder's empty and moving it solved the problem just trash it and be happy everything works. (It's not a proactive solution, but it is easy.)

Step 3: move the "/Library/Internet Plug-Ins/" folder to the desktop. If that works, start moving the plugins back into the (new) "/Library/Internet Plug-Ins/" folder one-by-one. This shouldn't fix the problem because a corrupt global plug-in would affect every account. So, if it does, it's probably just that plug-ins preference file that's corrupted, and removing it from the "~/Library/Preferences/" folder will hopefully do the trick.

Step 4: clear the Cache folders. This is a little involved, but it's my best guess for what will fix this. Make sure Fast User Switching is turned off and log out. At the Login screen enter ">console" (no quotes) as the username and hit Log In. That should take you to a text console login: prompt. Log in to the text console. Then "sudo rm -rf" the following directories: "~/Library/Caches", "/Library/Caches/", "~/Library/Icons" and "~/Library/Safari/Icons". Then logout and restart the machine. (Either just hit the restart button at the login screen, or, if its hidden, enter ">restart" as the username.)

Step 5: temporarily reset Safari's state. With Safari not running, move the ~/Library/Safari folder and ~/Library/Preferences/com.apple.safari.plist file to the desktop. If Safari runs fine after that, try moving the Safari/Bookmarks.plist into the new Safari folder. If it still runs fine, the easiest thing to do is accept that your Form Auto-fill data is gone and re-personalize Safari's preferences. This would have been step 2, but for the life of me I can't figure out why this would affect IE or FireFox.

Step 6: reset all preferences. This one's kinda drastic. Move the "~/Library/Preferences" folder to the Desktop. Logout and log back in. If the browsers work it's a corrupt pref file. So, start moving the files from Desktop/Preferences into Library/Preferences a few at a time, launching the browsers after each group to test them, the usual isolate-the-bad-file drill.

Hope this helps.

If it effects all browsers, I'd check the proxy settings. Under the Network pref pane, select the active network(s), and go to the Proxies tab and see if there's an HTTP proxy specified.

I had this problem recently with my PowerBook 667 running Tiger. I had to reboot about three times, cleaning out preferences and caches for all my browsers.

After that, it seemed to return to normal.

Holy cow! Thanks for the help.

I tried the simpler stuff first, then dove into Scott's list of suggestions (which should probably become a wikipedia page or something).

I worked through steps 1 through 5, none of which fixed the problem, though I learned some good stuff along the way. One fix to the instructions: in step 4, you have to change the login UI from "List of Users" to "User Name" or whatever it's called. I don't know if Fast User Switching was important or not.

Step 6 finally worked. Moving all the Preferences aside fixed the problem. Having identified the haystack, I was now faced with the challenge of finding the needle itself. After moving some files around, I realized that I would lose track of what I had moved where, so I made a copy of the entire Preferences folder so I would have a clean copy if things got messed up. The copy got stuck on com.apple.InterfaceBuilder.plist. Interesting!

I tried putting back all of the Preferences except com.apple.InterfaceBuilder.plist, and the browsers were still broken. I started again, and making the copy, it got stuck on com.apple.iMovie3.plist. Interesting! Why would the copy get stuck twice in almost the same place? By looking at the copied files themselves, I had my answer: they hadn't. They had both gotten stuck copying com.apple.internetconfig.plist! The asynchronous progress bars were displaying different statuses at the time of the freeze.

When I saw that file name, I knew I had the problem solved, because internetconfig is just where the problems were happening. I put back all of Preferences except that file, and everything works great!

I tried to look into the busted plist file, but I can't even "more" it without getting stuck. It's in the Trash now. Who knows if I'll be able to empty it!?

Anyway, thanks for all the help! You guys are the best!

I'm glad one of them worked. :)

If Fast User Switching is turned on, you can't get to the text console. The system will switch to a blank, blue screen and then bounce you back to the Login Panel. (Or it just hangs at the blue screen which tends to be frustrating enough that the irony is lost.)

com.apple.internetconfig.plist is really the System 7 era Internet Config preference file in disguise. It's literally a bunch of encoded-binary entries.

Anyways, glad we got it working again.

See? The Mac IS easier to use!