are possible to increase zoom??

[mustdave]

for now its 300% , can some how can increase more than that??

[Basilisk-Dev]

Under about:config set zoom.maxPercent to your desired maximum percentage.

It only seems to affect the maximum zoom value when zooming in with Control/Command + scroll wheel. When you use Control/Command + Shift + Plus the max value is still 300%.

[Moonchild]

When you use Control/Command + Shift + Plus the max value is still 300%.

You can control that with toolkit.zoomManager.zoomValues -- it has the specific steps listed from smallest to largest. you could add additional values to the end for even larger zoom levels, I think.