--- a/browser/components/extensions/parent/ext-pkcs11.js
+++ b/browser/components/extensions/parent/ext-pkcs11.js
@@ -34,29 +34,41 @@ this.pkcs11 = class extends ExtensionAPI
   getAPI(context) {
     let manifestCache = new DefaultMap(async name => {
       let hostInfo = await NativeManifests.lookupManifest(
         "pkcs11",
         name,
         context
       );
       if (hostInfo) {
+        // We don't normalize the absolute path below because
+        // `Path.normalize` throws when the target file doesn't
+        // exist, and that might be the case on non Windows
+        // builds.
+        let absolutePath = PathUtils.isAbsolute(hostInfo.manifest.path)
+          ? hostInfo.manifest.path
+          : PathUtils.joinRelative(
+              PathUtils.parent(hostInfo.path),
+              hostInfo.manifest.path
+            );
+
         if (AppConstants.platform === "win") {
-          // If the path specified in the manifest is not an abslute path,
-          // translate it relative to manifest's directory.
-          if (!PathUtils.isAbsolute(hostInfo.manifest.path)) {
-            hostInfo.manifest.path = PathUtils.normalize(
-              PathUtils.joinRelative(
-                PathUtils.parent(hostInfo.path),
-                hostInfo.manifest.path
-              )
-            );
-          }
+          // On Windows, `hostInfo.manifest.path` is expected to be a normalized
+          // absolute path. On other platforms, this path may be relative but we
+          // cannot use `PathUtils.normalize()` on non-absolute paths.
+          absolutePath = PathUtils.normalize(absolutePath);
+          hostInfo.manifest.path = absolutePath;
         }
-        let manifestLib = PathUtils.filename(hostInfo.manifest.path);
+
+        // PathUtils.filename throws if the path is not an absolute path.
+        // The result is expected to be the basename of the file (without
+        // the dir path and the extension) so it is fine to use an absolute
+        // path that may not be normalized (non-Windows platforms).
+        let manifestLib = PathUtils.filename(absolutePath);
+
         if (AppConstants.platform !== "linux") {
           manifestLib = manifestLib.toLowerCase(manifestLib);
         }
         if (
           manifestLib !== ctypes.libraryName("nssckbi") &&
           manifestLib !== ctypes.libraryName("osclientcerts") &&
           manifestLib !== ctypes.libraryName("ipcclientcerts")
         ) {

--- a/browser/components/extensions/test/xpcshell/test_ext_pkcs11_management.js
+++ b/browser/components/extensions/test/xpcshell/test_ext_pkcs11_management.js
@@ -106,16 +106,27 @@ async function setupManifests(modules) {
         `Loading of PKCS#11 modules is not supported on ${AppConstants.platform}`
       );
   }
 }
 
 add_task(async function test_pkcs11() {
   async function background() {
     try {
+      const { os } = await browser.runtime.getPlatformInfo();
+      if (os !== "win") {
+        // Expect this call to not throw (explicitly cover regression fixed in Bug 1759162).
+        let isInstalledNonAbsolute = await browser.pkcs11.isModuleInstalled(
+          "testmoduleNonAbsolutePath"
+        );
+        browser.test.assertFalse(
+          isInstalledNonAbsolute,
+          "PKCS#11 module with non absolute path expected to not be installed"
+        );
+      }
       let isInstalled = await browser.pkcs11.isModuleInstalled("testmodule");
       browser.test.assertFalse(
         isInstalled,
         "PKCS#11 module is not installed before we install it"
       );
       await browser.pkcs11.installModule("testmodule", 0);
       isInstalled = await browser.pkcs11.isModuleInstalled("testmodule");
       browser.test.assertTrue(
@@ -243,16 +254,22 @@ add_task(async function test_pkcs11() {
   await setupManifests([
     {
       name: "testmodule",
       description: "PKCS#11 Test Module",
       path: testmodule,
       id: "pkcs11@tests.mozilla.org",
     },
     {
+      name: "testmoduleNonAbsolutePath",
+      description: "PKCS#11 Test Module",
+      path: ctypes.libraryName("pkcs11testmodule"),
+      id: "pkcs11@tests.mozilla.org",
+    },
+    {
       name: "othermodule",
       description: "PKCS#11 Test Module",
       path: testmodule,
       id: "other@tests.mozilla.org",
     },
     {
       name: "internalmodule",
       description: "Builtin Roots Module",