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Why does v57.0.x freeze up and send the cpu to 100%?

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After reinstalling Windows 7 64-bit on my home PC I installed v57.0.2. The browser often freezes permanently, and the CPU is pegged to 100% because one of the firefox processes is eating up all the remaining CPU (85%+). Sometimes the only way to unfreeze the browser is to end the firefox processes, start it again, and do a Troubleshoot>Reset. But this is only a temporary fix because it will freeze up again after a while. This may happen several times a day.

After reinstalling Windows 7 64-bit on my home PC I installed v57.0.2. The browser often freezes permanently, and the CPU is pegged to 100% because one of the firefox processes is eating up all the remaining CPU (85%+). Sometimes the only way to unfreeze the browser is to end the firefox processes, start it again, and do a Troubleshoot>Reset. But this is only a temporary fix because it will freeze up again after a while. This may happen several times a day.

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That's pretty drastic!

First, please rule out the bug related to Accessibility Services. That is covered in the reply from philipp in the following thread: Firefox 57 hangs up.

We have bunch of general support articles with tips that might be useful:

One point that's interesting is that it sounds like your session after a Refresh is fine, the problem doesn't return until you close Firefox completely and start it up again. Is that what you notice?

Firefox has been a multiprocess application since around Firefox 49, and since Firefox 54 it may use four content processes. Firefox uses the first run after installation (or after a Refresh) to assess the system before going into multiprocess mode. So that suggest a test:

To help evaluate whether multiprocess is causing problems, or whether the same issue occurs with a single process, you could turn off multiprocess as follows:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box above the list, type or paste autos and pause while the list is filtered

(3) Double-click the browser.tabs.remote.autostart.2 preference to switch the value from true to false

Note: the exact name of the preference may vary, but it will start with browser.tabs.remote.autostart

At your next Firefox startup, it should run in the traditional way. Any difference?