I had a couple of extensions installed in ubuntu 19.04. After upgrading to 19.10 they are all disabled (I look them up in Tweaks app). Beforehand, I had installed them using a firefox extension, but now when I try to install the same items it is not possible, probably it finds the previous installations and refuses to do a new install. Thanks
Download the extensions you want from https://extensions.gnome.org/ Select the latest version of that extension.
Most of the time they will be in zip format so extract the file from the zip folder. Open the extracted folder and locate the metadata.json file. In that file, replace the shell-version with the one you currently have and save. Also copy the uuid and use it to rename the extracted folder.
After you've done this, copy and paste that extracted folder(with the uuid as it's new name) in the extensions folder located in .local/share/gnome-shell
Once you've done this, restart your gnome shell and your extensions should be working. Don't forget to enable extensions in the Tweaks app.