This extension somehow disabled copying in google docs which drove me nuts until I deleted it. I don't know why it did this.

Destructive add-on. When copying from Simplenote.com notes text longer than 10 lines, this app truncates it making looking like
_____________________
beginning of text
..............................
...the end
________________
The middle part just disappears.

Lately I have noticed in Firefox that the mouse-3 context menu, including the "copy video URl at current time" (CVUACT) item, does not appear. It turns out that the addon enable-selection somehow blocks the youtube context menu.

breaks many websites because it injects jquery code into each and every website. wrong approach!