Patch for bug 1676956 got backed out for failures on Android.
The test used to work before (until it got moved in bug 1649873), but was disabled on Android due to the existing global skip-if in xpcshell-e10s.ini (bug 1683157).

Without tests runs on Android, bug 1637059 may have introduced changes to the test file that breaks the test on Android.

Log + failure is at https://bugzilla.mozilla.org/show_bug.cgi?id=1676956#c4.

xpcshell.ini:toolkit/components/extensions/test/xpcshell/test_ext_webRequest_startup.js | Starting test_1
(xpcshell/head.js) | test test_1 pending (2)
"CONSOLE_MESSAGE: (info) 1608223577601	addons.manager	DEBUG	Application has been upgraded"
"CONSOLE_MESSAGE: (info) 1608223577602	addons.manager	DEBUG	Loaded provider scope for resource://gre/modules/addons/XPIProvider.jsm: ["XPIProvider", "XPIInternal"]"
"CONSOLE_MESSAGE: (info) 1608223577602	addons.manager	DEBUG	Starting provider: XPIProvider"
"CONSOLE_MESSAGE: (info) 1608223577602	addons.xpi	DEBUG	startup"
"CONSOLE_MESSAGE: (info) 1608223577602	addons.xpi	INFO	SystemAddonLocation directory is missing"
"CONSOLE_MESSAGE: (info) 1608223577611	addons.xpi	INFO	Removing all system add-on upgrades."
"CONSOLE_MESSAGE: (info) 1608223577611	addons.xpi	DEBUG	checkForChanges"
"CONSOLE_MESSAGE: (info) 1608223577611	addons.xpi	DEBUG	Loaded add-on state: ${}"
"CONSOLE_MESSAGE: (info) 1608223577612	addons.xpi	DEBUG	scanForChanges changed: false, state: {}"
"CONSOLE_MESSAGE: (info) 1608223577613	addons.xpi	DEBUG	Empty XPI database, setting schema version preference to 33"
"CONSOLE_MESSAGE: (info) 1608223577613	addons.xpi	DEBUG	No changes found"
"CONSOLE_MESSAGE: (info) 1608223577621	addons.xpi-utils	DEBUG	Synchronously loading the add-ons database"
"CONSOLE_MESSAGE: (info) 1608223577621	addons.xpi-utils	DEBUG	Starting async load of XPI database /data/local/tmp/test_root/xpc/p/extensions.json"
xpcshell.ini:toolkit/components/extensions/test/xpcshell/test_ext_webRequest_startup.js | JavaScript error: resource://gre/modules/addons/XPIInstall.jsm, line 669: Error: File resource://default-theme/ does not contain a valid manifest
xpcshell.ini:toolkit/components/extensions/test/xpcshell/test_ext_webRequest_startup.js | JavaScript error: resource://gre/modules/addons/XPIInstall.jsm, line 669: Error: File resource://default-theme/ does not contain a valid manifest
"CONSOLE_MESSAGE: (error) [JavaScript Error: "Error: File resource://default-theme/ does not contain a valid manifest" {file: "resource://gre/modules/addons/XPIInstall.jsm" line: 669}]"
"CONSOLE_MESSAGE: (error) [JavaScript Error: "Error: File resource://default-theme/ does not contain a valid manifest" {file: "resource://gre/modules/addons/XPIInstall.jsm" line: 669}]"
(xpcshell/head.js) | test run_next_test 1 finished (2)
Unexpected exception Error: File resource://default-theme/ does not contain a valid manifest at resource://gre/modules/addons/XPIInstall.jsm:669
loadManifest@resource://gre/modules/addons/XPIInstall.jsm:669:11
awaitPromise@resource://gre/modules/addons/XPIProvider.jsm:216:15
syncLoadDB@resource://gre/modules/addons/XPIDatabase.jsm:1656:19
startup@resource://gre/modules/addons/XPIProvider.jsm:2507:23
callProvider@resource://gre/modules/AddonManager.jsm:230:31
_startProvider@resource://gre/modules/AddonManager.jsm:601:17
startup@resource://gre/modules/AddonManager.jsm:825:14
startup@resource://gre/modules/AddonManager.jsm:3530:26
observe@resource://gre/modules/addonManager.js:87:29
promiseStartupManager@resource://testing-common/AddonTestUtils.jsm:975:34
test_1@test_ext_webRequest_startup.js:79:9
_run_next_test/<@/data/local/tmp/test_root/xpc/head.js:1621:22
_run_next_test@/data/local/tmp/test_root/xpc/head.js:1621:38
run@/data/local/tmp/test_root/xpc/head.js:768:9
_do_main@/data/local/tmp/test_root/xpc/head.js:239:6
_execute_test@/data/local/tmp/test_root/xpc/head.js:568:5
@-e:1:1
exiting test