I cannot be 100% certain but I'm confident I was using it not long after the 1.0 release. That'd put me at 2004. 19 years!
Although I did briefly switch over to Chrome when it was new and fast. Then switched back when Firefox had a major optimization pass.
What grinds my gears with all the people (whether Denuvo officials or elsewhere) that claim that it has no effect on performance: they only focus on average FPS. Never a consideration for FPS lows or FPS time spent on frames that took more than N milliseconds. Definitely not any look at loading times.
I'm willing to believe a good implementation of Denuvo has a negligible impact on average FPS. I think every time I saw anyone test loading times though, it had a clear and consistent negative impact. I've never seen anyone check FPS lows (or similar) but with the way Denuvo works I expect it's similar.
Performance is more than average framerate and they hide behind a veil of pretending that it is the totality of all performance metrics.
There was one extension I used in Chrome that I haven't found a Firefox replacement for, but I stopped trying to look a while ago and just live without it.
Was a specific kind of cookie manager: you could whitelist a set of websites to keep their cookies. Everything else would be deleted when you told the extension to do so.
Too many websites need cookies that stick around indefinitely. But I also don't want to delete everything everytime I close Firefox, because I may want to keep a website around for a few days without wanting to bother adding it to a whitelist.