diff --git a/extensions/spellcheck/src/mozInlineSpellChecker.cpp b/extensions/spellcheck/src/mozInlineSpellChecker.cpp
index f5cd6e7f3f2c..ace8b2ea5677 100644
--- a/extensions/spellcheck/src/mozInlineSpellChecker.cpp
+++ b/extensions/spellcheck/src/mozInlineSpellChecker.cpp
@@ -44,6 +44,7 @@
 #include "mozilla/Logging.h"
 #include "mozilla/RangeUtils.h"
 #include "mozilla/Services.h"
+#include "mozilla/StaticPrefs_extensions.h"
 #include "mozilla/TextEvents.h"
 #include "mozilla/dom/Event.h"
 #include "mozilla/dom/KeyboardEvent.h"
@@ -93,8 +94,6 @@ using namespace mozilla::ipc;
 
 static mozilla::LazyLogModule sInlineSpellCheckerLog("InlineSpellChecker");
 
-static const char kMaxSpellCheckSelectionSize[] =
-    "extensions.spellcheck.inline.max-misspellings";
 static const PRTime kMaxSpellCheckTimeInUsec =
     INLINESPELL_CHECK_TIMEOUT * PR_USEC_PER_MSEC;
 
@@ -564,18 +563,14 @@ mozInlineSpellChecker::SpellCheckingState
 
 mozInlineSpellChecker::mozInlineSpellChecker()
     : mNumWordsInSpellSelection(0),
-      mMaxNumWordsInSpellSelection(250),
+      mMaxNumWordsInSpellSelection(
+          StaticPrefs::extensions_spellcheck_inline_max_misspellings()),
       mNumPendingSpellChecks(0),
       mNumPendingUpdateCurrentDictionary(0),
       mDisabledAsyncToken(0),
       mNeedsCheckAfterNavigation(false),
       mFullSpellCheckScheduled(false),
-      mIsListeningToEditSubActions(false) {
-  nsCOMPtr<nsIPrefBranch> prefs = do_GetService(NS_PREFSERVICE_CONTRACTID);
-  if (prefs)
-    prefs->GetIntPref(kMaxSpellCheckSelectionSize,
-                      &mMaxNumWordsInSpellSelection);
-}
+      mIsListeningToEditSubActions(false) {}
 
 mozInlineSpellChecker::~mozInlineSpellChecker() {}
 
diff --git a/extensions/spellcheck/src/mozInlineSpellChecker.h b/extensions/spellcheck/src/mozInlineSpellChecker.h
index dae736d5147d..e3d0648cd5dd 100644
--- a/extensions/spellcheck/src/mozInlineSpellChecker.h
+++ b/extensions/spellcheck/src/mozInlineSpellChecker.h
@@ -165,7 +165,7 @@ class mozInlineSpellChecker final : public nsIInlineSpellChecker,
   RefPtr<mozilla::EditorSpellCheck> mPendingSpellCheck;
 
   int32_t mNumWordsInSpellSelection;
-  int32_t mMaxNumWordsInSpellSelection;
+  const int32_t mMaxNumWordsInSpellSelection;
 
   // we need to keep track of the current text position in the document
   // so we can spell check the old word when the user clicks around the
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index fed7b657e1d7..b4e4ce1db527 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -4299,6 +4299,12 @@
   value: false
   mirror: once
 
+# Maximum number of misspelled words in a text.
+- name: extensions.spellcheck.inline.max-misspellings
+  type: int32_t
+  value: 500
+  mirror: always
+
 # Whether the extensions can register a service worker on its own.
 # NOTE: WebExtensions Framework ability to register a background service worker
 # is not controlled by this pref, only the extension code ability to use
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index b952099c7613..20d57ff2cb3d 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -1004,11 +1004,6 @@ pref("print.print_edge_bottom", 0);
   pref("print.print_in_color", true);
 #endif
 
-// Pref used by the spellchecker extension to control the
-// maximum number of misspelled words that will be underlined
-// in a document.
-pref("extensions.spellcheck.inline.max-misspellings", 500);
-
 // Whether inserting <div> when typing Enter in a block element which can
 // contain <div>.  If false, inserts <br> instead.
 pref("editor.use_div_for_default_newlines",  true);