Addon works but ...

1. This addon's "homepage" link is for the addon "Alarm, Timer and Stopwatch by Brian" by (see https://addons.mozilla.org/en-US/firefox/addon/alarm-timer-and-stopwatch/). This gives a false impression that the linked page is maintained by THIS addon's author (as it should be)
2. Brian's addon is fully open-source and published on github (indirectly linked to from either that addon's "homepage" link or this one's. The direct link is: https://github.com/brian-girko/alarm/tree/master/v3). This addon's source is available only by downloading the xpi and extracting (I downloaded both xpis and did not notice anything suspicious while comparing them - however, I am a regular developer, not a security expert, and did not perform a full analysis anyway). Judging from the source code this one appears to be a fork.
3. This addon's description does not explicitly credit the original / note that it is a fork. It also does not describe the differences added.
4. This addon has less features than the original (hasn't merged updates). This one has Stopwatch + Timer. The original has since been updated and has Alarm + Stopwatch + Timer.

My rating was determined as follows: -1 for false impression in homepage link, -1 for not explicitly crediting original author / noting this is a fork in addon description and not describing the changes, +1 for addon working as described, -1 for not having code changes in a public repo (not req by Moz but still preferred by me), -1 for lack of alarm functionality.

No points were given for the lack of malicious code as that is a Moz requirement and something expected from all addons as standard behavior. (not to mention I did not fully review code and could have easily missed something).