That's surprising. Web sites can use scripts to intercept and repurpose many keyboard shortcuts (for example, changing Ctrl+B from opening the Bookmarks Sidebar to making text bold). However, if this is happening on all sites, it seems more likely that an add-on is the culprit. Add-ons can't ''directly'' replace built-in keyboard shortcuts, but they can inject scripts into the web pages (Content Scripts) to do it the same way web sites can. This is hard to track down, but if any of your add-ons are related to zooming text or images, you would want to check those. Otherwise, hmm, you didn't share a list of your add-ons in your original post, but you could add that to a future reply (here at https://support.mozilla.org/questions/1417169, not by email). Here's how: Open the Troubleshooting Information page. Either: * "3-bar" menu button > Help > More Troubleshooting Information * (menu bar) Help > More Troubleshooting Information * type or paste '''about:support''' in the address bar and press Enter Scroll down a few screens to the "Add-ons" section. Then you can select and copy the table that follows (not the entire page, please, that's too much information) using either Ctrl+c or right-click > Copy and then paste it into a reply. It will be messy, but we're used it.