If you installed the Zotero browser extension in 2022 or earlier (even if you uninstalled and reinstalled it recently), it can cause you to get proxy server errors like this one:
When you install the Zotero browser extension, it comes with proxy redirection enabled by default.
To resolve the problem, follow these steps for Chromium-based browsers or Firefox:
For Chrome, Edge, Brave and other Chromium-based browsers:
1. Click on the kebab menu, select Extensions > Manage Extensions
2. Click on the Zotero Connector’s ‘Details’
3. Select ‘Extension options’
4. Go to the Proxies tab and deselect ‘Enable proxy redirection’
1. Click on the hamburger menu and select 'Add-ons and themes'
2. Click on the ellipsis menu for the Zotero Connector and select 'Options'
3. Go to the Proxies tab and deselect ‘Enable proxy redirection’