It wasn't FireFox, but Netscape definitely was actively worked against.
> Am I misremembering this era?
Apparently.
But here is a link to refresh your memory.
https://bootcamp.uxdesign.cc/the-netscape-microsoft-browser-...
To save you a click:
"The Shell Execute Bug
However, Microsoft’s most significant tactic was the infamous “shell execute bug.” This bug caused some users to fail when trying to install Netscape, but it was not present when installing Internet Explorer, giving Microsoft yet another advantage. While Microsoft claimed the bug was unintentional, many believed it was a deliberate attempt to prevent users from installing Netscape. The bug caused significant damage to Netscape’s market share and cemented Microsoft’s dominance in the browser market."