Ooh! I like feeling useful! I will totally attempt to talk you through this.
Are you using Google Chrome? If not, I highly suggest it.
It is super, super easy to use extensions with Chrome. In fact, I just installed a lot of fun new ones this morning.
I still use FireFox for everything else, but I have Chrome all pimped out for Tumblr.
IMO, Missing E and Tumblr Savior are necessary requirements for a happy Tumbling experience. Missing E lets you reblog yourself, upload photos easier, wraps tags, copies tags, lets you make temporary bookmarks instead of liking posts, and a lot more.
Tumblr Savior blocks any posts with certain words in it. I’ve got mine set to block a lot of the ships that squick me out or even just silly things, like artists whose work I’m not fond of. I know some people who use it to block spoilers.