Now
The PlowShare Online Bible Study web application requires Firefox 45+ ESR (or W3C standards compliant browser). HTML5 and CSS3 compliance are required.
Firefox is the primary browser supported (for its longevity, stability, and continual standards compliance).
[Note: Making PlowShare function in every browser is not the Lord's calling on my life.]
Safari mobile (iPad) and desktop webkit browsers are the secondary platforms (Safari for Mac, Google Chrome).
Although Internet Explorer 10+ may work, it is not tested and no time is given to support it.
Back in 2003...2011
PlowShare was initially developed using IE 5.5 and Firefox 0.9. However, due to a continual lack of web standards in Microsoft Internet Explorer, support for the browser was dropped. PlowShare requires a web standards compliant browser like Firefox 10.0 or later. As of this writing, only Firefox is supported, although Google Chrome and Safari (Mac OSX, iPad, Win) work well also. Opera seems to work with every other version that it releases (due to its efforts to be IE compatible and standard compliant).