reinstalled firefox, now it appears. However, all got slow, more than 10s to open a page...

Make sure that Screenshots isn't disabled if it happens again. You can check these prefs on the [https://support.mozilla.org/en-US/kb/about-config-editor-firefox <b>about:config</b>] page. *extensions.screenshots.disabled = false *screenshots.browser.component.enabled = false ----- Start Firefox in <b>Troubleshoot Mode</b> to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if <b>hardware acceleration</b> or <b>userChrome.css</b> is causing the problem. *switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes *do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window *https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode *https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems *https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-or-cpu-resources *https://support.mozilla.org/en-US/kb/quick-fixes-if-your-firefox-slows-down ---- It is possible that your firewall or other security software blocks or restricts Firefox without informing you, possibly after detecting changes (update) to the Firefox application. Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full, unrestricted, access for Firefox and the plugin-container process and the updater process. See: *https://support.mozilla.org/en-US/kb/server-not-found-connection-problem *https://support.mozilla.org/en-US/kb/Firewalls *https://support.mozilla.org/en-US/kb/fix-problems-connecting-websites-after-updating