Merge pull request #752 from Zydrolic/add-note-to-read-me-ff-install

add the developer note below installing on firefox in README.md

Author: MaterArc

README.md

@@ -39,6 +39,9 @@ We're a browser extension for the Scratch website that makes Scratch look, work,
 There are multiple ways of installing.
 - Chrome: You can download from Chrome [here](https://chrome.google.com/webstore/detail/scratchtools/jjnpbalpllpfdpgplpbcbadkgdmleopm). Then just press the Add to Chrome button, and you've downloaded ScratchTools!
 - Firefox/Mozilla: You can download for Firefox [here](https://addons.mozilla.org/en-US/firefox/addon/scratchtools/). You can then just add it to Firefox, and then you have ScratchTools!
+> [!NOTE]
+> The Firefox version of Scratchtools is behind compared to the chrome version of Scratchtools due to technical difficulties. Until a solution is found, the Firefox version will remain behind.
+
 - Microsoft edge: You can download for Edge [here](https://microsoftedge.microsoft.com/addons/detail/scratchtools/aaidjeidbnhpjhblbianjeghjopbimmk). You can then just add it to Edge, and then you have ScratchTools!
 - Safari (macOS, iPadOS and iOS): You can build the extension by typing `make` for macOS, and `make ios` for the iOS app (you will have to sign it on  Xcode), make sure you have enabled Developer mode and allowed unsigned extensions.
 - GitHub: Download from GitHub [here](https://github.com/STForScratch/ScratchTools/zipball/master). If it downloads a `.zip` file, unpack it. Then, with the folder, go to `chrome://extensions`, make sure you have developer mode enabled (switch in the top right corner), and drag the downloaded folder onto the page. Make sure you've disabled other versions of ScratchTools.