You may want to wait a day and update to Firefox 3.6.17, due to be released later today.

• Download a new copy of the Firefox program
• Firefox 4.0: http://www.mozilla.com/en-US/firefox/all.html
• Firefox 3.6: http://www.mozilla.com/en-US/firefox/all-older.html
• Trash the current Firefox application to do a clean (re-)install
• Install the new version that you have downloaded

Your profile data is stored elsewhere in the Firefox Profile Folder, so you won't lose your bookmarks and other personal data.

Edit: Firefox 3.6.17 is released, so you can update now.

Thank you. I'm pretty much a computer idiot, so your answer isn't completely clear to me. Is each bullet point a different option? Do I trash the current Firefox application before installing something else?

I had a terrible time downloading the last time I did it. It took 4 times, and the new bookmark page lost half my bookmarks the first time I added a new one. Very frustrating. I've been very reluctant to change again, despite assurances such as the one above that I won't lose anything.

I just noticed that Firefox 3.6.17 has been released, so you can try to download that full version now.

If you want to backup your profile data then see:

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder

• http://kb.mozillazine.org/Profile_backup
• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox