--- a/toolkit/components/aboutmemory/content/aboutMemory.js
+++ b/toolkit/components/aboutmemory/content/aboutMemory.js
@@ -839,16 +839,20 @@ function makeDReportMap(aJSONReports)
                         "$1NNN)");
 
     // Strip null principal UUIDs (but not other UUIDs, because they may be
     // deterministic, such as those used by add-ons).
     path = path.replace(
       /moz-nullprincipal:{........-....-....-....-............}/g,
       "moz-nullprincipal:{NNNNNNNN-NNNN-NNNN-NNNN-NNNNNNNNNNNN}");
 
+    // Normalize omni.ja! paths.
+    path = path.replace(/jar:file:\\\\\\(.+)\\omni.ja!/,
+                        "jar:file:\\\\\\...\\omni.ja!");
+
     let processPath = process + kProcessPathSep + path;
     let rOld = dreportMap[processPath];
     if (rOld === undefined) {
       dreportMap[processPath] =
         new DReport(jr.kind, jr.units, jr.amount, jr.description, 1, undefined);
     } else {
       rOld.merge(jr);
     }

--- a/toolkit/components/aboutmemory/tests/memory-reports-diff1.json
+++ b/toolkit/components/aboutmemory/tests/memory-reports-diff1.json
@@ -22,16 +22,17 @@
 
     {"process": "P2 (pid 22)", "path": "p1 (pid 123)", "kind": 2, "units": 0, "amount": 33, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "p2 (blah, pid=123)", "kind": 2, "units": 0, "amount": 33, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "p3/zone(0x1234)/p3", "kind": 2, "units": 0, "amount": 33, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "p4/js-zone(0x1234)/p4", "kind": 2, "units": 0, "amount": 33, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "p5/worker(foo.com, 0x1234)/p5", "kind": 2, "units": 0, "amount": 33, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "explicit/window-objects/top(bar.com, id=123)/...", "kind": 0, "units": 0, "amount": 33, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "p6/z-moz-nullprincipal:{85e250f3-57ae-46c4-a11e-4176dd39d9c5}/p6", "kind": 2, "units": 0, "amount": 33, "description": "Desc."},
+    {"process": "P2 (pid 22)", "path": "p7/js-main-runtime-compartments/system/jar:file:\\\\\\temp_xyz\\firefox\\omni.ja!/p7", "kind": 2, "units": 0, "amount": 33, "description": "Desc."},
 
     {"process": "P3", "path": "p3", "kind": 2, "units": 0, "amount": 55, "description": "Desc."},
 
     {"process": "P5", "path": "p5", "kind": 2, "units": 0, "amount": 0, "description": "Desc."},
 
     {"process": "P7", "path": "p7", "kind": 2, "units": 0, "amount": 5, "description": "Desc."},
 
     {"process": "P8", "path": "p8/a/b/c/d", "kind": 2, "units": 0, "amount": 3, "description": "Desc."},

--- a/toolkit/components/aboutmemory/tests/memory-reports-diff2.json
+++ b/toolkit/components/aboutmemory/tests/memory-reports-diff2.json
@@ -23,16 +23,17 @@
 
     {"process": "P2 (pid 22)", "path": "p1 (pid 456)", "kind": 2, "units": 0, "amount": 44, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "p2 (blah, pid=456)", "kind": 2, "units": 0, "amount": 44, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "p3/zone(0x5678)/p3", "kind": 2, "units": 0, "amount": 44, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "p4/js-zone(0x5678)/p4", "kind": 2, "units": 0, "amount": 44, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "p5/worker(foo.com, 0x5678)/p5", "kind": 2, "units": 0, "amount": 44, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "explicit/window-objects/top(bar.com, id=456)/...", "kind": 0, "units": 0, "amount": 44, "description": "Desc."},
     {"process": "P2 (pid 22)", "path": "p6/z-moz-nullprincipal:{161effaa-c1f7-4010-a08e-e7c9aea01aed}/p6", "kind": 2, "units": 0, "amount": 44, "description": "Desc."},
+    {"process": "P2 (pid 22)", "path": "p7/js-main-runtime-compartments/system/jar:file:\\\\\\temp_abc\\firefox\\omni.ja!/p7", "kind": 2, "units": 0, "amount": 44, "description": "Desc."},
 
     {"process": "P4", "path": "p4", "kind": 2, "units": 0, "amount": 66, "description": "Desc."},
 
     {"process": "P6", "path": "p6", "kind": 2, "units": 0, "amount": 0, "description": "Desc."},
 
     {"process": "P7", "path": "p7/b", "kind": 2, "units": 0, "amount": 3, "description": "Desc."},
     {"process": "P7", "path": "p7/c", "kind": 2, "units": 0, "amount": 4, "description": "Desc."},
 

--- a/toolkit/components/aboutmemory/tests/test_aboutmemory3.xul
+++ b/toolkit/components/aboutmemory/tests/test_aboutmemory3.xul
@@ -321,16 +321,19 @@ 0.00 MB (100.0%) -- p4\n\
 └──0.00 MB (100.0%) ── js-zone(0xNNN)/p4\n\
 \n\
 0.00 MB (100.0%) -- p5\n\
 └──0.00 MB (100.0%) ── worker(foo.com, 0xNNN)/p5\n\
 \n\
 0.00 MB (100.0%) -- p6\n\
 └──0.00 MB (100.0%) ── z-moz-nullprincipal:{NNNNNNNN-NNNN-NNNN-NNNN-NNNNNNNNNNNN}/p6\n\
 \n\
+0.00 MB (100.0%) -- p7\n\
+└──0.00 MB (100.0%) ── js-main-runtime-compartments/system/jar:file:///.../omni.ja!/p7\n\
+\n\
 0.00 MB ── p1 (pid NNN)\n\
 0.00 MB ── p2 (blah, pid=NNN)\n\
 \n\
 End of P2 (pid NNN)\n\
 P3\n\
 Other Measurements\n\
 \n\
 -0.00 MB ── p3 [-]\n\
@@ -416,16 +419,19 @@ 11 B (100.0%) -- p4\n\
 └──11 B (100.0%) ── js-zone(0xNNN)/p4\n\
 \n\
 11 B (100.0%) -- p5\n\
 └──11 B (100.0%) ── worker(foo.com, 0xNNN)/p5\n\
 \n\
 11 B (100.0%) -- p6\n\
 └──11 B (100.0%) ── z-moz-nullprincipal:{NNNNNNNN-NNNN-NNNN-NNNN-NNNNNNNNNNNN}/p6\n\
 \n\
+11 B (100.0%) -- p7\n\
+└──11 B (100.0%) ── js-main-runtime-compartments/system/jar:file:///.../omni.ja!/p7\n\
+\n\
 11 B ── p1 (pid NNN)\n\
 11 B ── p2 (blah, pid=NNN)\n\
 \n\
 End of P2 (pid NNN)\n\
 P3\n\
 Other Measurements\n\
 \n\
 -55 B ── p3 [-]\n\