If anyone uses Firefox, it is possible to disable websites from knowing about any clipboard-related events. Go to about:config, search for dom.event.clipboardevents.enabled and set it to false. Done.
It's pretty sad that something as security sensitive as browser settings requires trusting random strangers on the internet or digging through source code to understand what's going on.
If Mozilla made a chrome UI for those settings, they'd be accused of adding bloat to Firefox, creating complex options that confuse users, and making Firefox harder to use than Chrome-based browsers. I've noticed that open source really can't win in that department, so power user settings are put out of sight and out of mind, or are eliminated completely.
TBH, the I personally think the UI is fine, but it's annoying to have so many places to look for settings.
Chromium/Chrome have chrome://flags, which is basically the same UI, but all of the options have a few sentences explaining what they do.
I still miss Opera; they were the only browser developer who didn't take the "Users are stupid and easily confused" approach to browser development.
Old Opera was amazing, and incredibly fast. For a while there on pre-Android and early Android phones, Opera rendered the fastest out of all the mobile browsers.
Possibly, but does Mozilla actually care about accusations of bloat or poor usability?