Rated 5 out of 5 stars
Sorry, I know that bug reports are not supposed to come here but I didn't find any better place. Let's hope the developer reads the users' reports.
First known bad:
UA:"Mozilla/5.0 (X11; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0 SeaMonkey/2.51a1"
Last known good:
Same UA and localization (or lack thereof) as above, except that the "last good" build had Firefox 54.0a1 with SeaMonkey 2.51a1 which is more normal.
Using Addons Recent Updates 0.1.7 in both cases.
Symptom: Even though the extension's pref is set to 366 days, I only see a couple of days' worth of updates in about:addons
*Edit* After installing the development version from https://github.com/Infocatcher/Addons_Recent_Updates/ it works again (see details on the issues page mentioned in the developer's reply).
Fixed in development version:
(will be released after more careful testing)
P.S. Also there is "Support site" link on extension page.