I can attest to that! While I never reached the upper echelons of virality that other browsers in recent memory have, I had much the same experience with Waterfox. Right place, right time gave it its initial user base: posting about a 64-bit build of Firefox on the Overclock.net forums. It hit the right time as people were starting to switch to 64-bit Windows and upgrading their hardware to match

I think that first week the project got 50k downloads! I was of course only 16 so had no concept of what to do but just keep getting new builds out - after all I made the builds because I couldn’t find anyone who would consistently and regularly do so.