Sometimes `sessionStorage` is defined but accessing it is an error. In these instances we can't use capturing (because error-recovery involves reloading the page but the reloaded page won't know that startup is failing). FIXME: probably shouldn't start HyperFrameset if `sessionStorage` unavailable - seems to only be 'file:///' access on Firefox.
Sometimes `sessionStorage` is defined but accessing it is an error.
In these instances we can't use capturing (because error-recovery involves
reloading the page but the reloaded page won't know that startup is failing).
FIXME: probably shouldn't start HyperFrameset if `sessionStorage` unavailable -
seems to only be 'file:///' access on Firefox.

meekostuff/HyperFrameset,meekostuff/HyperFrameset,meekostuff/HyperFrameset