I spend days (literally) looking for an add-on that could download high resolution files from YouTube (1080p+ video streams, as well as their respective audio streams). Unlike newbies, I didn't want an add-on bundled with third party crappy tools to joing the files for me, I can do that myself if necessary without compromising my privacy, safety and sanity. Unfortunately, after trying absolutely ALL YouTube download add-ons available on Moziila's site (except the obvious junk that use external sites for downloading), I didn't find any, until I tried this older add-on again, and what a surprise, it does do the job perfectly!

I had dropped this add-on before, because (1) it didn't show the high resolution files and (2) the download button didn't show up (it was added to the Page, but the DIV block was hidden, requiring me to manually move it out of that hidden block, what was too much trouble for a limited add-on).

Well, it just happens that both problems are solvable! First of all, this is THE ONLY add-on that shows high resolution links for downloading without using unnecessary third party external spyware, all I had to do was activate the options on its, yeah, options Page (why they come disabled by default is a mystery, but I guess the author got tired of newbies complaining that some video and audio files are downloaded as separate files, when that's the way it actually should be, as that's how YouTube delivers them).

Secondly, the "invisible button" is a problem of YouTube's new front-end design. Using other add-ons (I'm using Enhancer for YouTube, which allows adding a script to force YouTube to use the old front-end). Voilà, add-on working nicely!

I simply cannot believe that absolutely all other add-ons are used to exploit naïve users into installing spywares into their browsers! They claim that it's impossible to download high resolution files from YouTube (on of them going as far as saying that YouTube only delivers incomplete URL, so only itself and external tools could retrieve them). Shame on them all!

Anyway, thanks to the authors of this add-on, for keeping it alive despite Mozilla's and Google/YouTube's wild changes of mood and for being fair to their users!

Suggestion: you could move the button out of YouTube's Page and put it in the context menu or on a toolbar button, so it wouldn't depend of YouTube's front-end anymore.