I don't know about problems loading WP with Firefox, as I have been using Sea Monkey lately. I had been using Firefox as my default browser, but I had problems with it when running videos, like on Hulu, and YouTube. The programs ran way too slow and stuttery. A relative had loaded several other browsers on my PC for me to tryout. I had tried Sea Monkey before without problems, so I am using that again. The videos run better on Sea Monkey, with only occasional slow downs and stuttering. I have a slow DSL speed, as that's all I am paying for, so I don't expect a lot, but the Firefox problems drove me nuts. Watching videos on it wasn't much better than dial-up. Sometimes non video pages also loaded way too slow on Firefox, too. I had the latest version, so I don't know what could be causing the problem. I will mostly use Sea Monkey instead now. I also have Chrome and Internet Explorer on here, but never use them, because they are more often targeted by malware. I may check them out sometime, just out of curiosity, though. The first browser I ever used was Internet Explorer many years ago, and I had a lot of problems with it back then. Although I may "explore" it, I don't think I would want to use it on a regular basis.
As for your own problems with Firefox, I have come across stories on the I-net lately about other people having problems with it. I think you are right to try another browser for now. I still sometimes use Firefox for non video stuff, as I have a lot of links on my "Super Page" there. So far, Sea Monkey doesn't have the Super Page add-on, and I am still trying to get all my links and bookmarks copied onto Sea Monkey. One thing that has been a big help is my ProtoPage account. I have a huge number of my bookmarks on bookmark widgets on my homepage there. Once I had that site bookmarked onto Sea Monkey I had access to most of my links. I also recently put the link to my old Yahoo page onto Sea Monkey. I hardly used it any more when I started using a different web mailer, and ProtoPage, but lately I have been unable to get into my new email account, so now I am back to using my old Yahoo email account. I don't like that they track you, but I need a working email account to keep in touch with relatives.
I am glad we have access to other browsers, and I hope you don't have any more problems.