This is a very bizarre problem. Basically I can't install any Firefox addon neither on my desktop OR may laptop. I noticed this issue just couple of days ago. When I try to install any addon normally, from a link, it tells me that the addon can't be installed because the file is corrupt. Tried several addons, all same problem. On my desktop AND on my laptop. On my desktop I'm running ver. 103, but on my laptop I still had ver. 102.1, so there is no Firefox update issue. When I try to install addon from xpi file, it tells me that I have no permission to open that file and that's it. I tried to take ownership of that file but it didn't solve the issue I tried to disable my AV program, but it didn't do anything. On my laptop, I tried to refresh FF, no help. I tried to start FF in safe mode, same problem. I created new profile, same issue. Eventually, I totally uninstalled FF, removing program itself, removing Appdata folder and even registry entry. Installed fresh copy of FF, same problem exists. Then, I noticed one thing. When I tried to sync fresh FF installation on my laptop, it synced everything, EXCEPT for addons. So, something is preventing me doing anything regarding addons. Themes install just fine. I've struggling with this problem since yesterday and at this point I totally ran out of any fresh ideas how to solve this issue, thus posting here. I'll appreciate any fresh idea as what to do next. Thanks