Linux Mozilla tips

(I plan to offer more tips in the future. The first tip is about an annoying problem installing Java.)

Problem: error message

The program must close to allow a previous installation attempt to complete. Please restart
No amount of restarting will fix this problem. The problem is caused by Mozilla not cleaning up after installing an .xpi file, such as jre.xpi, the Java run time environment.
Mozilla leaves a file called xpicleanup.dat in it's home directory. As root, you must remove the file:
# rm /usr/lib/mozilla-0.9.3/xpicleanup.dat
Sometimes it isn't clear where Mozilla has been installed. To find the directory, do
$ locate component.reg
Each directory with a component.reg is probably a Mozilla installation. Some may be obsolete. Remove the file from all of them.
Commentary: Is there a bugzilla entry for this? I don't know. Bugzilla doesn't allow full text searching of it's archives, and I don't know what keywords to look for...

Problem: no Java

Java sometimes doesn't install when you click on the puzzle piece. To install Java reliably, get a copy of jre.xpi. For example, there is one at Download it. Then, as root, start Mozilla. (Before starting Mozilla, you may want to set your umask to 002.) Open the jre.xpi file as if it was a file.
Linux stuff.