Are these macros key combinations or something more complex?

Did they invoke a notification? Anything interpreted as a notification request no longer opens a popup, but triggers a speech bubble icon in the address bar. Unlikely scenario, but possibly relevant.

Are you using Private Browsing when this happens? Can you try normal browsing mode and see if the issue persists?

The 2 macro keys are simply a text of 2 emails rather than type it in everytime. Macro keys in Firefox will not display in url, logins or any txt spaces in any webpages. I'm not in private browsing but I did try it & macros doesn't work in private browsing. I've tried safe mode firefox & without addons running. Still no joy with firefox.

So the macros basically just paste text. Is this like fetch stored text then ctrl +v to paste? I've checked some of the documentation but a user-defined macro could be anything. (ctrl +v should work, of course, as should mouse pasting, i am just looking to get a feel for this if necessary.)

Since the issue is occurring only with Firefox, had you installed any custom user .js or .css?

Can you test this on another computer, or with a separate Firefox install (for instance, Firefox Developer Edition, which won't affect your current Firefox installation or profiles)?

Maybe the issue has a similar solution to this? https://support.mozilla.org/en-US/questions/952115

Other things: Do you have the latest G Hub update? 2019-11-25 https://support.logi.com/hc/en-us/articles/360025298133

Maybe one of these boilerplate Logitech suggestions:

   Restart both computer and keyboard, by powering them both OFF and back ON
   Test to different computer (to replicate the issue)
   Try downloading and installing the Logitech Setpoint Software and use it to restore the keyboard into default.

None of my other ideas are leading anywhere. I hope something here is a fix, or at least diagnostic.