zilla isn't a word reserved to Mozilla, there are other thing using this word, like godzilla, where mozilla name came from.
"Remember, it's spelled N-E-T-S-C-A-P-E but it's pronounced: Mozilla, the Mosaic Killer Godzilla".
some sources: http://fredericiana.com/2007/04/15/mosaic-killer/
> it was internally named Mozilla (Mosaic-Killer, Godzilla) by Jamie Zawinski
https://en.wikipedia.org/wiki/List_of_company_name_etymologi...
> Mozilla Foundation – from the name of the web browser that preceded Netscape Navigator. When Marc Andreessen, co-founder of Netscape, created a browser to replace the Mosaic browser, it was internally named Mozilla (Mosaic-Killer, Godzilla) by Jamie Zawinski.[110]