[wp-trac] [WordPress Trac] #53624: Gutenberg "Add block" preview loads empty for the first time in Firefox

[WordPress Trac]

#53624: Gutenberg "Add block" preview loads empty for the first time in Firefox
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 Reporter:  nextend_ramona  |      Owner:  (none)
     Type:  defect (bug)    |     Status:  new
 Priority:  normal          |  Milestone:  Awaiting Review
Component:  Editor          |    Version:  5.7.2
 Severity:  normal          |   Keywords:
  Focuses:                  |
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 In Firefox browser when adding a new block, the "first" block preview is
 always blank. It only loads when you hover on another block (and back). I
 was only able to reproduce this in Firefox, but not in Chrome.

 WordPress: 5.7.2
 Theme: Twenty Twenty-One Version: 1.3
 Other plugins installed: none
 Browser: Firefox 89.0.2
 Browser extensions: disabled
 OS: Windows 10


 Steps to reproduce:
 1. Create a new post
 2. Click on the blue "+" (Add block) icon
 3. Hover on a block icon, like "Paragraph"
 4. A preview opens, and it's empty. See: https://imgur.com/hfoTdGP
 5. Hover on the "Heading" then come back to the "Paragraph". Now it loads.
 See: https://imgur.com/NQHHKqN

 It's not just the "Paragraph" block's icon, it happens with all icons that
 are on the side.

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Ticket URL: <https://core.trac.wordpress.org/ticket/53624>
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