I have been using it for years, NO PROBLEM Rated 4 out of 5 stars

I really don't understand 1 star ratings complaining about having to pay for using certain features like converting videos. I never needed such feature(s), and I am a HEAVY user who installed this years ago. Obviously, I'd be happier if everything was free, although -seriously- you won't miss any features here without the need to pay for extra ones.
Besides, there are other nice little programs out there which will convert all type of files without a problem.

Apart from that, this add-on was featured 7th in the list of the slowest add-ons for firefox, apparently slowing it down up to 33%. I reckon Firefox have been crashing a lot in their latest versions, particularly when queuing more than 10 videos (so I suspect this add-on is involved in the crashes). However, I recently changed to WaterFox and it works fine. I never tried queuing more than around 20 videos yet (the time when I could queue more than 100 without a problem seem long gone), but so far so good.

I am still looking for a different light weight add-on capable of doing what this one does, Unfortunately, none so far seems to match it. So, even though DownloadHelper is a heavy weight with its more than 700kb, I'll stick to it for now and I thank the developers for it.

This review is for a previous version of the add-on (4.9.8.1-signed). 

Rated 4 out of 5 stars

I have been using it for years, usually works fine. However, bear in mind that it will slow down FF and, for power users, it may make it crash. However, a normal user shouldn't have a problem. I have tried different video downloaders and they don't come even close (except for Video Myxa, perhaps, more light weight and similar -if not so sharp- features). If you could make a lite version not slowing down FF considerably, I'd give you 5 stars, definitely ;D

This review is for a previous version of the add-on (4.9.8.1-signed). 

Rated 4 out of 5 stars

Have been using it for more than a year now with no problem. It's not compatible with some websites but it's fine overall. You have to pay to convert, although you can do that easily with an external program. It'd be handy to have the option to click any of the mouse bottons directly on the video for downloading.

This review is for a previous version of the add-on (4.9.3.1-signed).