firefox: Update to 77.0

Changelog:
New
    Pocket recommendations, featuring some of the best stories on the web, will appear on the Firefox new tab for our users in the UK. If you don窶冲 see them, you can turn on Pocket articles in your new tab, follow these steps.

    WebRender continues its roll out to more Firefox for Windows users, now available by default on Windows 10 laptops running on Nvidia GPUs with medium (<= 3440x1440) and large screens (> 3440x1440).

    You can view and manage web certificates more easily on the new about:certificate page.

Fixed
    Various security fixes.

    A number of features have been fixed to improve Firefox accessibility.
        The applications list in Firefox Options is now accessible to screen reader users.
        Some live regions previously didn't report updated text with the JAWS screen reader. This issue has been fixed.
        Date/time inputs are now no longer missing labels for users of accessibility tools.

Changed
    The browser.urlbar.oneOffSearches preference has been removed. To hide one-off search buttons uncheck search engines on the about:preferences#search page

Security fixes:
#CVE-2020-12399: Timing attack on DSA signatures in NSS library
#CVE-2020-12405: Use-after-free in SharedWorkerService
#CVE-2020-12406: JavaScript type confusion with NativeTypes
#CVE-2020-12407: WebRender leaking GPU memory when using border-image CSS directive
#CVE-2020-12408: URL spoofing when using IP addresses
#CVE-2020-12409: URL spoofing with unicode characters
#CVE-2020-12410: Memory safety bugs fixed in Firefox 77 and Firefox ESR 68.9
#CVE-2020-12411: Memory safety bugs fixed in Firefox 77

(ryoon)