browser.tabs.captureVisibleTab not working in firefox for mv3

[hans_squared]

It’s a permission problem:
Firefox MV3 treats all host permissions as optional.

You need to jump through a few hoops to use tabs.captureVisibleTab()

1. Install the test extension:
   captureVisibleTab.zip (1.5 KB)

2. Click the action icon to download a screenshot of the active tab.
   Because the extension doesn’t have the “<all_urls>” permissions yet, the extension console displays:
   TypeError: browser.tabs.captureVisibleTab is not a function
   Enable the “<all_urls>” permission in the Add-ons Manager:
   

   

3. Click the action icon again.
   Again, the extension console displays:
   TypeError: browser.tabs.captureVisibleTab is not a function
   Reload the extension:
   

   

4. Click the action icon again.
   The extension now creates the file “captureVisibleTab.png” in the Downloads directory.
   

   

Notes:

• For the sake of simplicity, the test extension forces the user to enable the “<all_urls>” permissions manually, and reload the extension manually. A finished extension could do this with browser.permissions.request() and browser.runtime.reload()
• I don’t know why you have to reload the extension after enabling the “<all_urls>” permissions.
  If you think this is a bug, please consider reporting it on https://bugzilla.mozilla.org/
• I don’t know if Firefox will distinguish between required and optional host permissions once the “optional_host_permissions” manifest key has been implemented.
  See manifest.json > optional_permissions > Host permissions
• browser.tabs.captureVisibleTab() returns a data URL.
  Firefox 118.0 can’t download data URLs, so the test extension converts the data URL to a blob, then converts the blob to an object URL, and downloads the object URL.