using disabled="true" enables document.oncontextmenu behavior
I disable right click context menu on the body element. <body onload="document.oncontextmenu = function() {return false};">
Now if I use disabled=true on various elements (<input type="text" disabled=true>, <textarea disabled="true">). Right click displays a context menu. This behavior does not happen on other browsers, and probably is a regression, but I don't know when it stopped working.
The context menu is disabled as long as the disabled="true" is not present.
Alla svar (4)
Maybe setting the control to disabled makes it a "no JavaScript events" zone, so your script never sees the right-click?
You could check Firefox 60 ESR Portable Edition to see whether this is a change since Firefox 60. That runs out of the download folder so it doesn't touch your settings. However, you do need to exit out of regular Firefox in order to run it.
It was broken in that version also (60.6.1.esr). Just for clarity I am using the latest verion 66.0.2.
Hmm, you could check whether anyone has already reported it as a bug (or requested changing it): https://bugzilla.mozilla.org/