Getting there... Rated 4 out of 5 stars

1. Sometimes videos download slowly for no apparent reason. When downloading the same quality with FlashGot or the userscripts.org's "Download YouTube Videos as MP4" the same quality downloads at the speed you'd expect from your connection. The links are different to one another but it's the same quality option and size that each method is offering yet this addon seems to go at a snail's pace for some videos (usually for the lower quality ones). For example a 5MB low quality file took 2m37s when the highest quality of that same video took only 10 seconds (33MB).
— An option to give control on how to download the YT would be great. Either show the generic FF download popup (Open/Save File) that also has a FlashGot option or allow some direct way to let an ext. download manager grab the link. (Submitted)

2. BUG: The user defined folder option seems to be creating 2 files each download. One 0KB file and the second being the actual file with its filename having appended a "-1" to the end of it. This does not occur when using the other default download location options offered or when using the Select folder each time option (using the same folder I'd want as my user-defined one). Windows/FF 24.0a2 Aurora.
— FIXED

3. Would be nice if the Detect all possible download links button under each YouTube would toggle the window open and closed. Currently just opens it.This has the potential to be the best Firefox YouTube downloader. Would like to see it happen.
— (Submitted)

This review is for a previous version of the add-on (0.2.2). 

1. When you download a low quality video file, YouTube assumes you have low bandwidth and thus the download speed is low. If you want to check the real speed, copy the generated link and paste it in an external download manager. And for sure the link that this extension creates is exactly similar to the other extensions except the signature part.

2. Fixed here
https://github.com/inbasic/iaextractor/issues/523.

3. Please open up a bug for it!
https://github.com/inbasic/iaextractor/issues