Can't view XHTML Web sites, can anyone help?

I can't view web sites with the xhtml type. I get a "The connection was reset" error. I have a Mac with Firefox 9.0.1 and I keep it up to date. Hubby has an old PC with a current Firefox and xhtml sites won't load on his computer either. I'm positive something is "off" with Firefox. I don't believe I have a bug.

Long story short, I compared information about those sites with my favorite sites that will download. The sites that failed to load were all the "application/xhtml+xml" types; all successful sites were html types.

In troubleshooting the past few days, I accidentally saved one of the xhtml sites as a separate Safari link/file. With I opened the file, an old version of Safari popped up and the site worked. All those xhtml sites work on Safari.

I've researched several technical sites on the Internet (including Firefox/Mozilla) and searched AW trying to figure out how to fix Firefox myself, but either they don't tell me how to fix it or if they do, I just don't understand all the technical goo. Add-ons or plug-ins that mention "xhtml" are so full of gobblygook I don't have a clue which one, if any, might work.

Can anyone point me in the right direction? Thank you!

Here's one of the sites. Thank you both for trying.

Medievalist: Most importantly, I'm having NO problem with AW and all the controls look normal. Whew!

I have a satellite DSL connection so data downloads are fast.

When I was trying to figure out what the problem was, I compared the "Page Information" (under the "Tools" in the bar above) between all the pages of the sites that failed against several that worked. Every page that failed showed "application/xhtml+xml" types and all those that worked showed type of "html."

Tirjasdyn: I have my Firefox set to clear the cache every time I close it. Plus, I've manually cleared it too.

Here are a couple more Web sites that will not load: One, and two.

I'm sorry for the delay in getting back to you. Thank you for any ideas.

Charles Farley, thank you for your ideas. I've been all through Firefox and searched using a search engine to find out how to turn off the script debugging or anything like that. I can't find anything other than to download software like an add-on. I've been through every bit of software in the Mac to try to find the script debugging. I'm in the realm of messing with the "deeper", more intricate, software than I should be fiddling in. I don't want to cause a worse problem.

Makes NO sense! I think I'm going to give up on it. Thank you all so much for taking your time to help. Perhaps sometime in the future during an update, something will download that will make these work.

Charles Farley: I think I've reached my limit for delving into this. I pulled up that Web site you referenced, but I saw it was only for Windows/XP-type software. I sure appreciate your help!

Tirjasdyn: My QuickTime plugin is up to date. Still no difference. At one time today, I thought the encoding might have something to do with it. I learned a lot today about that, but that still didn't make a difference.

Thank you both for trying!

Excellent ideas! Thank you, Charles Farley and Medievalist. I'll look into those. Perhaps just getting rid of the Firefox and starting over is the way. Thank you again.

I deleted Firefox, but I couldn't find the "library" though. I downloaded another Firefox and ... no change.

Thank you all though for your ideas.