Certainly my fav add-on for YouTube.
Unfortunately 2-3 weeks now, this add-on has begun to bug and cause incredible amounts of lag on Firefox, and I always end up typing "about:performance" in URL bar only to once again see this add-on going sky high on 'energy impact'.

And it wont stop unless I disable this add-on... And if I enable it, a few minutes or hours later, the same thing will happen again.

So yeah, this is definitely a must-fix.

edit: Is it possible that this add-on is not compatible with some other add-on or script? Maybe, cuz I have 36 enabled add-ons and 41 or so scripts installed in Violentmonkey.

But still, I honestly doubt it has anything todo with the add-ons, bcs basically nothing has changed in the past 2 months. (small changes)

The only thing that's changed is that I added all these java scripts. But I still highly doubt it has todo with that, simply because this bug begins to happen out of the blue on it's own, while I'm NOT on youtube. (but I do* have youtube videos open in new tabs, so I'm not sure)

So far, it has happened while I was browsing sites other than YouTube.

lmk if you need more info. Maybe you changed something recently? Maybe it was bcs of Firefox update? Really hard to say.

> Free and Effective
> High Customization with option toggle
> Database import/export with sync feature
> Search feature with visit count

fantastic addon but it hasnt worked for a couple of weeks now, FF is up to date and it looks like watchmarker is. I loaded https://youtube.com/new to see if i was using old site but still nothing

I really like this extension, I would give it 5 stars if 1. it didn't show the videos watched on mobile as just the length of the video instead of the title and 2. I could go through the history in the extension to delete the dumb stuff, because I use it to catalogue progress watching all of certain channels. Otherwise, this is my favorite extension next to adblock.

Good

Great addon, a must-have if you're using YouTube on a regular basis.
Question: is there any chance for a mobile release?

ok,ok,u said you're swamp with work,and can't do this for CHROME,now you're at home CORONIA VIRUS IS EVERYWHERE,SURELY,SURELY WE CAN FIND THE TIME,IT NOT LIKE YOU'RE GOING ANYWHERE AREN'T WE??

***UPDATE 3-31-2020***
Switching to new theme fixed it! Thank you. I don't like the new theme but as we all know they will be switching to it eventually so I'll just deal with it.

This add-on was working fine for me and then it was updated (yesterday?) and no longer does anything. I've tried uninstalling and reinstalling and syncing the cache and it shows the videos I've watched on the settings page but it no longer marks them when on YouTube when trying to select the next video that I want to view. I wish there was a way to roll back to the prior version.

*** UPDATE - 03\30\20 ***
Simon,
You are truly a scholar and a gentleman. First time any developer on the Firefox Add-On board actually responded to my review; but I am glad you are "alive" and came out of slumber to patch this. It is now beautiful and YouTube has a bad habit of recommending videos I have already watched MONTHS ago. Your GRAY overlay with WATCHED text is AWESOME; because I code while I listen \ watch YouTube, so this makes it easier for me to avoid realizing I am re-watching something TWO minutes in. We MUST stop these YouTube creators from dipping 2, 3, 4, 5, 10, 100X for the same videos, hahaha... Thank you and now all we need is a way to auto-sync history across all our machines with a single account. I am too lazy for Manual Export\Import.... FIVE STARS !!!

*** OLD REVIEW - 03\24\20 ***
Developer needs to update this add-on; but it is possible they have not tested it recently with Firefox, since it has not been updated for over a year. It is an AWESOME idea; but does not work correctly with Firefox 74.0. All thumbnails appear with a grey overlay above it with the text WATCHED in some cases. It is an obvious alignment \ overlay issue; so most likely YouTube "broke" it and this needs to be fixed ASAP. If this is fixed, then I will upgrade to FIVE stars; because it is needed, so now I am off to find another add-on.

To start I need to tell how much i love this addon! Saying that sadly in the new layout it is not working perfectly! For some strange reason when this is enable the thumbnails in the front page it seems stretched, distorted and double size of the normal! I really hope for some update because I can't imagine myself not have it! (I will change my rating to 5 Stars if you solve this problem) Thanks!

Update:
PERFECT!!! Now works like a charm, thank you for the quick fix!
As I have promise I change my rating a 5 stars!
Regards!

It breaks the thumbnails on the home page, otherwise it works fine.

good because it allows exporting everything and importing it later, and it is actually base64 encoding so we can edit it with text editor maybe, hope extension for chrome and opera, bad because actually shows wrong videos in sidebar on right being watched, misalignment, but luckily this sidebar can be hidden via another extension called Youtube Enhancer

I just started using this. I also have the bug with the double-sized thumbnails but since I never use the Youtube starting page and the issue is not present in a channel's Videos page, it does not bother me too much.
I honor the idea of this add-on, as this is basically a must have.

Two questions or feature requests, though:

1. I would really like to be able to manually mark videos as "watched" and be able to de-mark them. Not sure how this could be implemented, GUI-wise, but I think it would be a very great feature!

2. Currently, it's sufficient to click a video to get it marked as "watched". Wouldn't you consider it more intuitive if a video only gets marked when watched "completely" or at least to 2/3, 3/4, 9/10? I know that's a bit philosophical and probably tricky to implement. Just asking. :)

This addon is godsend. However the latest YouTube update broke it. On hover / scroll the video thumbnails double in height every now and then.