the location marker is ok :) Rated 5 out of 5 stars
"Thanks for your message. One question, if you open the Rain Alarm configuration window manually (right click on the icon), does it show a location marker on the map or not?" Yes, a little red balloon with a black point inside appears in the map, marking the selected position with some accuracy.This review is for a previous version of the add-on (1.2.3). This user has 4 previous reviews of this add-on.
Thank you again, I found the problem in the mean time. You are also welcome to send an e-mail next time you encounter an issue. The reason is that Mozilla tries to keep issue reports separate from ratings.