it has distracting timer end pop-up in center of the screen. Minimum timer countdown is 1 minute.
No remaining time is visible in the status bar, just an icon (that's maybe FF thing and can't be changed by add-ons).

Can't realistically use this, the gray tone of the icon is practically invisible on a dark toolbar. I decided to try some different themes, even. The icon can be more visible, but it lacks contrast. Still, not useful for me as a result.

This plugin is like democracy. Sometimes it works, sometimes it doesnt. Mostly it doesnt. Shame.

Everyday I have to reset the alarms from on to off then back on again before it works right.

At first it looks fine, but in fact the the timer is stuck to one tab, so if you switch tab or close the tab that you started the timer with, it will break the whole thing.