As of MicroBlocks 0.5, MicroBlocks runs in Chromium-based web browsers, either Google's Chrome browser or recent versions of MicroSoft's Edge. (Each of them offers an experimental Chromium feature known as "WebSerial API" to communicate with the microcontroller.) This can be helpful in school, library, and other settings where it is difficult to install application programs.
As long as the computer has one of the supported browsers and a USB port, you can run MicroBlocks!
To run MicroBlocks in the browser visit:
https://microblocks.fun/run/microblocks.html
Note: Be sure to use HTTPS, not HTTP, otherwise MicroBlocks won't be able to connect to the microcontroller.
The browser version of MicroBlocks cannot yet install the MicroBlocks firmware on your microcontroller, which is required before you can program it through the browser. For now, it is easiest to use the stand-alone MicroBlocks app to install the firmware. If you have a micro:bit, Calliope mini, or AdaFruit microcontroller, you can also install the firmware by downloading the appropriate precompiled virtual machine from:
then dragging and dropping it onto the USB drive for your microcontroller.
Or if you select "Upgrade firmware" from the gear menu, you can download the firmware file from the browser and take advantage of the "save" dialog box to select the microcontroller board as the destination for the saved file, which will actually copy it onto the board.
Connect your microcontroller to the computer with a USB cable, then click on the USB icon and select "connect" from the menu:
That will bring up a dialog box listing the available serial ports. On some platforms you will see your microcontroller listed with two different variations (as shown below); either one will work.
If the browser connects successfully, a green circle will appear behind the USB icon:
Use the file menu to save and open files:
In the File Open dialog, the computer button will allow you to navigate to the file you saved. You can also open a MicroBlocks file by dropping it onto the MicroBlocks browser window: