Originally Posted by Martinus2u
fwiw I have found that recently firefox or one of its plugins occasionally lags with cpu usage spiking up to 100% on one core. kill-all firefox followed by a restart cures the issue. I have not found a way to trigger the issue at will.
commenting myself, the reason for this behaviour seems to be a memory leak or so. I've just noticed a firefox process using up 6 GB (out of 8 GB). After killing and restoring all sessions it came down to 340 MB. version is 20.0.