I'm developing an office addin product for excel (using microsoft's javascript api for office) that can be installed to run locally in excel workbooks as well as in office web i.e. user's online workbooks under his/her ms365 account. For testing the addin performance in office web, i'm currently trying out different browsers. There is a shortcut key to my addin that should open the addin taskpane. The shortcut doesn't conflict with any firefox or excel office web shortcut (even if it did, there should be a prompt according to microsoft's documentation). The problem is, when i load a workbook and press the shortcut key combination, the addin taskpane doesn't open. There is no error in console either. I tried setting the security.enterprise_roots.enabled = true assuming this could be due to certificate trust issue but that didn't solve it. More interestingly, the shortcut does work in firefox once after many retries and this is completely random - at least i couldn't identify when it works and why. It is very rare and may be once in 100 tries. I tried loading a sample addin provided by microsoft to test shortcuts (you can also use it) from here: https://github.com/OfficeDev/Office-Add-in-samples/tree/main/Samples/excel-keyboard-shortcuts If i load the manifest.xml in any office web excel workbook (as described in the sample above) in firefox, it worked the first time i.e. the prompt appeared (as the sample shortcut CTRL + ALT + 1 had a conflict with existing office excel shortcut for number formats dialog) and the shortcuts from both addins were working at this point (interesting). It means the sample addin shortcuts and my addin shortcut started to work briefly. Then again i pressed CTRL + F5 to test again, and none of the addin shortcuts were being picked up. My addin shortcut simply does nothing, and the sample addin shortcut opens excel's number format screen. If i reset the excel shortcut preference in the workbook using the search bar, it should show the conflict prompt for the sample addin, but it doesn't and rather loads the number format dialog. Please note that none of these behaviors are present in chrome and edge, where everything works as expected and documented by Microsoft - for both my addin and the sample. The taskpane opens as soon as i press the shortcut key for my addin or the sample's. I think firefox somehow ignores or doesn't remember the addin shortcuts most of the time. That's why it does nothing with my shortcut as it is not mapped to any excel or browser action. And it opens the number dialog for sample ignoring the sample shortcut because excel has an action against it. This also explains why both addin shortcuts work when one of them works as firefox starts to remember shortcuts for that session. What doesn't explain is why firefox doesn't store it all the time or why it keeps ignoring? If you want to reproduce, please try with the sample from microsoft. And please let me know if I can help in any way to identify the problem. Sorry for the very long message. I'm eagerly waiting for your response.