I opened the Browser Console, cleared it, and put it next to my Firefox
window. Then I typed an expression in the Web Console and hit enter. The instant
I did so an error appeared in the Browser Console:
NS_ERROR_UNEXPECTED: Component returned failure code: 0x8000ffff (NS_ERROR_UNEXPECTED) [nsIPrefBranch.getIntPref] utils.js:555:0
That utils.js:555:0
is a link, taking you to that specific line of that file:
WebConsoleUtils._usageCount = Services.prefs.getIntPref("devtools.selfxss.count");
Apparently something’s seems to be up with this devtools.selfxss.count
pref. I
opened about:config to see if I could figure out what.
It turned out that this pref was missing! So I right-clicked, and chose “New >
Integer”, entered devtools.selfxss.count
as the pref name and 0
as the
value.
It worked!
Then I researched what this pref is all about, and found
https://bugzilla.mozilla.org/show_bug.cgi?id=994134#c89:
What does this option exactly do and does setting it to 100 completely
disable this feature or making the message just less likely to appear?
The selfxss prevention works by counting the number of times you have used the
console, and turning off paste protection when you cross a certain number,
which is at the moment 5 (the number also stops incrementing after that).
Alternatively, when you type "allow pasting" into the console when the prompt
comes up, this pref is set to a number >5.
Setting it to any number more than 5 should fix this. 100 is just a high
enough number that it will be resilient to all change.
The question now is why it was missing.
You could check if you’re having the same problem. Otherwise this at least might
be helpful to track down your problem.