I’ve Googled around and as far as I can tell, fridge is just a shortened version of refrigerator. They both mean (essentially) the same thing. So why the D?
You mean the Frigidaire?
Except that D isn’t before the G.
I always just assumed it was phonetic. There’s a D in there to my ears.
“Fige” reads like: Fry’g or Fri-shay to me.
Say Frigidaire 10x fast. Then say it 10x fast without the “aire”.
Spelling it with a “D” makes it clear that the “G” is palatal, not gutteral.
“Fridge” is a household appliance.
“Frig” is a slang term for a sex act.
Euphony. Some words change their spelling and pronunciation in order to be better pronounced or understood.
The “d” comes the same place as the “tion” in “congressional”
What?
Fridge is /frɪdʒ/ in IPA.
Notice it includes a [d] sound.
Likewise in badge, edge, nudge, etc.
-dge is just the standard spelling for the J sound (IPA: /ʤ/) at the end of words. Consider also words like “judge,” “bridge,” “badge,” etc. So when the word got shortened to one syllable, the spelling changed to fit the standard orthography.
Words with J at the end are more common now, but even they often get pronounced more like the s in “measure” (IPA: /ʒ/).
You may notice the similarities in the IPA symbols. That’s because those two sounds are similar. To change from that sound in measure to a J sound, you, well, add a /d/, same as the difference between SH and CH is an added /t/ sound: /ʧ/ for CH vs. /ʃ/ for SH. This is called an affricate, as you release the pressure from the first sound into the second, which is why the IPA tends to merge them into one symbol–though it’s not incorrect to use separate symbols.
Now I’m going to start calling it Fri-shay! ha ha
Seems legit.
Now, about picnicking… 
I didn’t notice the forum, and actually thought the OP would be about William “The Refrigerator” Perry (a.k.a., “The Fridge”) and to what extent he improved the legendary defense (a.k.a., “D”) of the 1985 Chicago Bears.
Never mind …
I had a very similar reaction to the thread title – I thought it was about Perry, and how well (if at all) he learned the Bears’ defensive playbook.
Good lord, are we doomed to obsess about this team forever? 
Yes we are. It is the reason I opened the thread and I’m a Giants fan first.
Yeah, and why isn’t it “nitpic”?
Yes:
Frigidaire was founded as the Guardian Frigerator Company in Fort Wayne, Indiana, and developed the first self-contained refrigerator, invented by Nathanniel B. Wales and Alfred Mellowes in 1916. In 1918, William C. Durant, a founder of General Motors, personally invested in the company and in 1919, it adopted the name Frigidaire.
The brand was so well known in the refrigeration field in the early-to-mid-1900s, that many Americans called any refrigerator a Frigidaire regardless of brand.
Same principle. The sound was added for euphony.
And the IPA describes the end result, not the cause.
No sounds were added. Sounds were removed from refrigerator to get fridge, but no sounds were added at all.
“Fridge” makes perfect sense, but now explain why the shortened form of vegetable is veggie. The double ‘g’ would usually indicate a hard /g/ sound. Perhaps we’ve been spelling it wrong and it should be vedgie.
My Irish friend calls it “veg”, which maybe should be “vedge.” 