Still works fantastic on both desktop and Android. Saves screen real estate! Only breaks a few sites but can whitelist.

I just installed it tested it for 5 sites and it worked for all of them in the same way. Very useful. Often, websites' fonts are too small, so I need zooming. On mobile, I can zoom only a specific portion of the screen, leaving the layout unchanged, but for some reason, browser makers don't expose that feature unless the computer has a touch peripheral. So, if I use the regular zooming to enlarge the text, the fixed top toolbar becomes huge, sometimes taking 30% of the screen. I think "hover to show" is an elegant solution for that on desktop.

And this is my first time seeing "verified". Mozilla says that they charge for the review but does not say how much. Was it expensive?

Simply the best add-on of this kind, and I tried many!

It works wonder and does a far better job than any other element blockers, including Adblock Plus and uBlock Origin which are actually failing miserably at this particular task.

Sticky Ducky is straightforward and very effective. The presets are clever and to the point. I can't believe it has so few users. Many thanks to the author, my browsing experience has never been better <3

After reading the enthusiastic reviews, I've been disappointed and perplexed by my own experience. In the course of many months (currently with Win10) I've yet to see one placeholder or any evidence that the add-on is doing anything. I do see many unwanted stickies, which remain untiI I remove them with the use of the Kill Sticky add-on. Disabling Sticky Ducky does not cause any changes that I can see. (I can't consult the developer as there's no contact information.)
Update:
Reading the Developer Response [below], I'm more perplexed than ever. The extension's toolbar icon provides options for "when to show sticky elements," still including (the one I chose) "When hovering over." This is consistent with the instructions when I installed it [perhaps removed now] referencing placeholders--and makes no sense without the existence of placeholders.

Amazing!

After manually 'hiding' 'sticky elements' with Adblocker Ultimate's Right-Click--Block-Ad-On-This-Website one, by one, by one.....I now have this wonderful add on instead.

Does *exactly what it needs to---hides / gets rid of all of what I call "static elements" that have taken over significant portions of SO MANY webpages the last few years.

These unmoving portions of webpages are, by and large, one of the WORST designs in G.U.I., sometimes leaving only ~ half of the webpage free to scroll and view what you went there for in the first place!

One big caveat: The permissions for this add-on are all-seeing, and I doubt they actually have to be to make an extension like this functional. But unmovable static webpage elements are SO UNBELIEVABLY ANNOYING I'm willing to risk this developer is honorable.

EDIT: After the developer's good response, it is clear that the permissions requested are, indeed, necessary for the add-on to operate as it should. Truly a wonderful program for Firefox users :)

EDIT Dec'20 --- I am still in LOVE with this extension. As another user mentioned, I'm certain there are lots of users (I'd hazard, literally millions) who HATE unmovable webpage elements as much as I do and don't know such an amazingly useful extension exists. A hundred thank yous to the developer! :)

Geweldig, eindelijk van al die bewegende meuk af.
Wat mij betreft 10 sterren.

Great extension, works in all the websites I tried so far!

Amazing. It works on every page, and cleans the page of extraneous crap.
'After Scrolling Up' works ideally for me, the stickied functions are all there when I want them but hidden when I don't clearly up screen real estate but there are options to cover however I imagine most anyone would want such elements to function.

There have been a handful of similar add-ons in the past but none of them worked particularly well.
This one is perfect, works everywhere and works however you want it to.

This extension is hands down one of the absolute best basic browsing quality of life improvements.
I'm sure there are lots of people who hate sticky elements, but have no idea this extension even exists.

This is the first time I've logged in to submit a review. Because this add-on satisfies my need to remove sticky elements so exactly.

There are other add-ons out there, like Kill Sticky, that allow you to selectively remove sticky elements per page. But you have to repeat the "hiding" action every time you visit a given site. And then there's uBlock Origin, which allows you to remove elements permanently. But then again, you have the hassle of creating rules for every page. And if you want to reveal elements for some reason on some occasion, you have the hassle of either finding and deleting a rule you may have created some time ago, or disabling AdBlock completely for the visit, which obviously may be undesirable.

This add-on allows you to take the default position "I hate sticky elements, so hide them when they exist. Even if it's the first time I've visited this particular site. Don't make me tell you every time."

That basic "hide by default" behaviour would be enough of a Unique Selling Point to recommend this add-on. But the way it implements selective revealing of sticky elements when they are actually important to you is even better. I have my prefs set to "reveal elements when I scroll up" at present. And this seems to work, because it reveals stickies when I scroll a significant distance. (Not like the poorer implementation some pages have, where if you scroll up even 1 pixel to try and read a line that's just off the top edge of the page, you instantly get a sticky header that obscures even more of the text instead.)

The only way this add-on could be better would be if there were some setting that allowed you to turn off sticky elements full stop. And where revealing said elements would involve deliberate user interaction with the add-on. (A "reveal sticky elements for this session" button, or similar, as an alternative option to "reveal by scrolling up.") But it's quite usable enough as is. And is head and shoulders above those add-ons mentioned above that make you selectively hide sticky elements by hand, which takes away the good of having an annoyance-hiding add-on.

PS: One of the other reviews mentions that this add-on needs a Whitelist. Not sure if it's been added as a result of that review, but the version I'm using does allow you to Whitelist pages permanently, if the implementation of sticky elements on that page is important to you.

Elegant and works on every website I've tried so far. The only thing I'm worried about is the amount of JavaScript used. Does having the entire Underscore.js library affect performance?

could you add an option to make the addon automatically change the attribute so that the element stays on it's original place instead of hiding it?