diff --git a/toolkit/components/osfile/modules/ospath_unix.jsm b/toolkit/components/osfile/modules/ospath_unix.jsm
index 4199ead628b2..119e982b0e75 100644
--- a/toolkit/components/osfile/modules/ospath_unix.jsm
+++ b/toolkit/components/osfile/modules/ospath_unix.jsm
@@ -165,7 +165,10 @@ exports.split = split;
 // The case of %3b is designed to match Services.io, but fundamentally doesn't matter.
 var toFileURIExtraEncodings = {';': '%3b', '?': '%3F', '#': '%23'};
 var toFileURI = function toFileURI(path) {
-  let uri = encodeURI(this.normalize(path));
+  // Per https://url.spec.whatwg.org we should not encode [] in the path
+  let dontNeedEscaping = {'%5B': '[', '%5D': ']'};
+  let uri = encodeURI(this.normalize(path)).replace(/%(5B|5D)/gi,
+    match => dontNeedEscaping[match]);
 
   // add a prefix, and encodeURI doesn't escape a few characters that we do
   // want to escape, so fix that up
diff --git a/toolkit/components/osfile/modules/ospath_win.jsm b/toolkit/components/osfile/modules/ospath_win.jsm
index 98cab2c65ab7..9c5a7b30d552 100644
--- a/toolkit/components/osfile/modules/ospath_win.jsm
+++ b/toolkit/components/osfile/modules/ospath_win.jsm
@@ -310,7 +310,10 @@ var toFileURIExtraEncodings = {';': '%3b', '?': '%3F', '#': '%23'};
 var toFileURI = function toFileURI(path) {
   // URI-escape forward slashes and convert backward slashes to forward
   path = this.normalize(path).replace(/[\\\/]/g, m => (m=='\\')? '/' : '%2F');
-  let uri = encodeURI(path);
+  // Per https://url.spec.whatwg.org we should not encode [] in the path
+  let dontNeedEscaping = {'%5B': '[', '%5D': ']'};
+  let uri = encodeURI(path).replace(/%(5B|5D)/gi,
+    match => dontNeedEscaping[match]);
 
   // add a prefix, and encodeURI doesn't escape a few characters that we do
   // want to escape, so fix that up
diff --git a/toolkit/components/osfile/tests/xpcshell/test_file_URL_conversion.js b/toolkit/components/osfile/tests/xpcshell/test_file_URL_conversion.js
index 4ef1fbce9bda..3ec42065bdb8 100644
--- a/toolkit/components/osfile/tests/xpcshell/test_file_URL_conversion.js
+++ b/toolkit/components/osfile/tests/xpcshell/test_file_URL_conversion.js
@@ -54,7 +54,7 @@ function run_test() {
     '/test;+%',
     '/test?action=index/',
     '/test\ test',
-    '/punctuation/;,/?:@&=+$-_.!~*\'()"#',
+    '/punctuation/;,/?:@&=+$-_.!~*\'()[]"#',
     '/CasePreserving'
   ];