As to the marriage records - it depends entirely on the database as to whether it will go and find the relevant spouse and link to that person, when no "marriage fact" already exists. Some do, and some don't (and on some other databases - such as the California divorce index - trying to link to an existing fact actually wipes out information, by changing "divorce from John Doe" to a generic "divorce" that is linked only to the person whose profile you have open).
The best way to do this is to create the marriage fact first, in which case the system generally will link to that. But be aware, it will try to link to the FIRST marriage fact in the timeline, so if this is a second marriage, it will try to link to the earlier one. In that case, if the second spouse has only this marriage, you should save to the second spouse in order to get it to link to the correct marriage (for both spouses).
I have no information about your FF questions - sorry, I don't use that browser.