[wp-trac] [WordPress Trac] #52133: TinyMCE editor doesn't load properly when initializing on Visual Tab (Firefox)

[WordPress Trac]

#52133: TinyMCE editor doesn't load properly when initializing on Visual Tab
(Firefox)
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 Reporter:  metalandcoffee  |      Owner:  (none)
     Type:  defect (bug)    |     Status:  new
 Priority:  normal          |  Milestone:  Awaiting Review
Component:  TinyMCE         |    Version:  5.6
 Severity:  normal          |   Keywords:
  Focuses:                  |
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 I've noticed that since updating to WordPress 5.6, TinyMCE editors within
 my custom metaboxes will sometimes fail to load/initialize when using the
 ''Firefox browser''. This only happens when the editor is initializing on
 the **Visual** tab. If I switch to the **Text** tab and then reload the
 page, the editor initializing normally. Please see the attached video for
 a clear understanding of what the issue is (firefox-bug-issue.mov). This
 screen recording will show that when you first go to the post, the TinyMCE
 editor initializes properly. But if you refresh the page, then the editor
 isn't initialized at all. It doesn't always happen like this. Sometimes
 I'll go to a post edit page and it's not initialized from the start.

 Theory:
 I say that this "sometimes" happens because it's almost like the tinymce
 js resources are loading too slow or too fast. This isn't a browser
 caching issue either because if I hard refresh the page, it still depends
 on how fast the resources are loading as to whether or not the TinyMCE
 editors will be properly initialized or not.

 I've confirmed that this was working fine on WordPress version 5.5.3.

 Steps to reproduce:
 I attached a file called "test-code.php" which will add a metabox with the
 TinyMCE editor to the 'post' post type.
 1. Add test code to theme or plugin.
 2. Open Firefox.
 3. Migrate to post edit page.
 4. See if you are able to click inside of the TinyMCE editor on the Visual
 tab.
 5. Refresh the page and repeat.

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Ticket URL: <https://core.trac.wordpress.org/ticket/52133>
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