https://searchfox.org/comm-central/rev/77f980a5aeac0a1aef7285bcfea6e64241fc0263/suite/editor/base/content/editor.js#1851-1856,1890-1893

      // Reduce the undo count so we don't use too much memory
      //   during multiple uses of source window
      //   (reinserting entire doc caches all nodes)
      try {
        editor.transactionManager.maxTransactionCount = 1;
      } catch (e) {}

      // Restore unlimited undo count
      try {
        editor.transactionManager.maxTransactionCount = -1;
      } catch (e) {}

These blocks are performed before and after updating the WYSIWYG editor for newer source code. However, I don't understand it wants to keep undoable only the updating.

I'll remove nsIEditor.transactionManager in bug 1768315, therefore, SeaMonkey needs to replace them with a call of editor.enableUndo(false) and editor.enableUndo(true). Then, the calls of the XHTML path between them are not necessary.

Bug 1792764 - Make comm-central stop using nsIEditor.transactionManager since it'll be removed

nsIEditor.transactionManager will be removed soon and its user is now only
SeaMonkey which want it to clear undo/redo transactions of editors. For doing
that, we can use nsIEditor.clearUndoRedo() now.

Note that the purpose of ExecuteJSTransactionViaTxmgr() will be invalid
after nsIEditor.transactionManager is removed. Therefore, this patch removes
it and the UI to run it too.

Comment on attachment 9299713 [details] [diff] [review]
Patch

LGTM. Thanks. There are a few minor formatting issues I have with some if the comments and I would like to keep the locale variable for the release branch but I will fix this up for check-in.

Thank you. I'll remove transactionManager of nsIEditor soon in m-c.

Hi, I'll land https://phabricator.services.mozilla.com/D160008 in a couple of days. Land the patch as soon as possible.

Thaks for the heads up. I will put it in our build patches queue for wip stuff till I land it. No need to delay the removal.

Thank you. I'll land it.

Pushed by frgrahl@gmx.net:
https://hg.mozilla.org/comm-central/rev/c693be030e90
Make suite stop using nsIEditor.transactionManager. r=frg