browser(firefox): use separate web processes for different contexts (#1975)

Author: yury-s

browser_patches/firefox/BUILD_NUMBER

@@ -1 +1 @@
-1086
+1087

browser_patches/firefox/preferences/playwright.cfg

@@ -3,6 +3,13 @@
 // Use light theme by default.
 pref("ui.systemUsesDarkTheme", 0);
 
+// Increase max number of child web processes so that new pages
+// get a new process by default and we have a process isolation
+// between pages from different contexts. If this becomes a performance
+// issue we can povide custom '@mozilla.org/ipc/processselector;1'
+//
+pref("dom.ipc.processCount", 60000);
+
 // Do not use system colors - they are affected by themes.
 pref("ui.use_standins_for_native_colors", true);