My Sony T1 works for very basic web browsing and it has pinch zoom. It is better if web site is set up for browsing from phone or tablet. Highlight a word for definition and one of the options in tree that pops up is Wikipedia. My Kobo touch web browser is unusable with latest firmware but was sort of usable with the prior firmware.
Kobo doesn't seem interested in developing a better web browser so it would have to be open source browser per your inquiry.
This topic should be moved to Kobo Developer's Corner.
https://www.mobileread.com/forums/forumdisplay.php?f=247