Ok, I FINALLY figured it out.
Here's what to do:

1. Find your wanted chrome extension (I'll use PreMiD for example)
2. Copy the link
3. Go to Chrome Extension Downloader
4. Click download. Then .CRX file will download.
5. Go to CRX Extractor
6. Select your downloaded .CRX file from your computer, or drag and drop
7. Click "Get Source Code". A .ZIP file with raw exntension file will start downloading
8. Unpack it to whatever location you like (eg. desktop)
9. Go to opera://extensions , switch on "Developer mode" in the top right corner, click on "Load unpacked", search for upacked .CRX extension folder and select it
   You're done!
   Hope it'll help some other people with this problem.

Hello. I just want to leave my suggestion for the workspaces. If there's something playing in workspace 1, and then switch to another one, there should be a little icon that shows something is playing in that workspace (because right now there's nothing like this and if you have many workspaces, you might not remember in which one there's something playing). I hope this will be implemented.

Hello. I just want to leave my suggestion for the workspaces. If there's something playing in workspace 1, and then switch to another one, there should be a little icon that shows something is playing in that workspace (because right now there's nothing like this and if you have many workspaces, you might not remember in which one there's something playing). I hope this will be implemented.

Ok, I FINALLY figured it out.
Here's what to do:

1. Find your wanted chrome extension (I'll use PreMiD for example)
2. Copy the link
3. Go to Chrome Extension Downloader
4. Click download. Then .CRX file will download.
5. Go to CRX Extractor
6. Select your downloaded .CRX file from your computer, or drag and drop
7. Click "Get Source Code". A .ZIP file with raw exntension file will start downloading
8. Unpack it to whatever location you like (eg. desktop)
9. Go to opera://extensions , switch on "Developer mode" in the top right corner, click on "Load unpacked", search for upacked .CRX extension folder and select it
   You're done!
   Hope it'll help some other people with this problem.

also, when i downloaded the extension itself to a .CRX file, double clicking on it, aswell as drag and drop to opera extension page won't work either

@leocg it still doesn't work for me. although it works on other accounts. i tried manually grabbing extension folder from opera's user files on that account, to my main account, but it still doesn't work.

Hello. I've used opera for a long time before on my old pc, and then everything with "install chrome extensions" was fine. Then, when I got new pc, I installed opera, and then opera gx (when it came out). In first months chrome extensions were installing normally, but recently I tried to download PreMiD addon, so I clicked "add to opera" button, it took me to extensions page, but then nothing showed up. I tried reinstalling opera gx aswell as opera (it's not working on regular opera too), but nothing happened either. And it comes to every chrome extension, not PreMid only. Any solutions?