That has not been my experience, or I would probably not be satisfied with Firefox on Android. I just checked and saw no difference between Firefox and Chrome starting to load a page.
First page load takes 10-30 seconds, and after that Firefox is fast and snappy.
However, my computer at work doesn't have this problem (and runs the same version of Ubuntu, i.e. 18.04.1)
Perhaps I should investigate this better, for instance by looking at system load, memory, and perhaps by monitoring system calls using strace.