One of the options (if the addon is an xpi) is to do a file -> open and locate the file and that should fix it.
They're supposed to be in .xpi format, not .jar
I thought theme is a kind of those addons. sorry
MR is just the right thing I'm looking for,it at last gives me a "Install" Button~~Also have a look at MR Tech [1]
Thank you guys very much!!
